NBSIR 88-3721

Flow of Molecules Through

Condoms

Charles M. Guttman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Gaithersburg, MD 20899

October 1987

Annual Report

Contract No. FDA 224-79-5023, Mod 16

L. Schroeder, Contract Officer

Food & Drug Administration

Office of Science & Technology

12000 Wilkins Avenue

Rockville, MD 20852

Prepared for. n Tmh MMiutMnt »
I ,
NBSIR 88-3721

FLOW OF MOLECULES THROUGH

CONDOMS

Charles M. Guttman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Gaithersburg, MD 20899

October 1987

Annual Report

Contract No. FDA 224-79-5023, Mod 16

L. Schroeder, Contract Officer

Prepared for; Food & Drug Administration

Office of Science & Technology

12000 Wilkins Avenue

Rockville, MD 20852

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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Abstract

An apparatus for the measurement of flux of small molecules through whole

condoms has been developed. It is shown that the experiment can measure

diffusion constants as low as 10"^^ cm^/s or a single pinhole as small as .4

micrometers in the condom. For pinhole measurements this is shown to be a factor of 10 better than current ASTM testing methods on the basis of flow

considerations only. Analysis of the experimental data show the difficulties

in making unambiguous determinations on the mechanisms of flow. Further

experiments are necessary to distinguish between large holes and small holes

and fluxes due to diffusion and those due to pinholes. These results suggest a more careful study of fluxes through condoms is necessary to assure that a particle about .1 micrometers cannot pass through the condom.
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1

I . Introduction

The use of condoms as a barrier to the spread of the AIDS virus has been

the topic of a number of recent discussions. One recent study has considered

whether a herpes virus, a virus simiiiar in size to the AIDS virus, can get

through a condom^

For a condom which does not suffer catastrophic failure, two mechanisms

are available for molecules to flow through the latex membrane.

1. Flow through pores or pinholes in the condom membrane.

2. Diffusion of the molecules through the condom membrane.

This project was under taken to model and measure the flow through latex

condoms and to relate this flow to either flow through pinholes in the condom

or diffusive flow through the condom membrane.

II. Modeling .gfUllpw Through Condoms

In the discussion that follows we shall compute and discuss the flux

through a condom arising from capillary or pinhole flow and the flux from

diffusion as extremes of possible flow mechanisms though the membranes.

A. Capillary or Pinhole Flow.

If one has a pinhole in the membrane then a particle can pass through this

pinhole. We shall first consider what are the important mechanisms and

parameters affecting transport of particles through pinholes before we make

model calculations of flow through pinholes.
2

1. Pinhole Description

For modeling purposes to be presented later in this report we shall

consider flow through pinholes as described by flow through a single capillary

or a distribution of capillaries of uniform cross section throughout their

length. It is clear that a realistic pinhole may have varying non- circular

cross section along its length. This fact complicates the interpretation of

the measurements of flow through the condom.

2. Particle Size Effects

Generally, flow through pinholes will be independent of the particle size

for particles smaller than the smallest radius in the pinhole. As the particle

size approaches that of the smallest radius in the pinhole, we expect to obtain

increased flow velocity of the particle^ until the particle reaches the size of

the pinhole's smallest radius. For particles larger than the smallest radius of

the pinhole we get no particle flow at all.

3. Pressure Effects

Increasing the pressure head increases the flow through a pinhole in an elastic material since 1) The pressure head is proportional to flow in a rigid

capillary and 2) the pressure head extends the rubber. The latter effect

increases the pinhole size and decreases the thickness of the rubber, both of

which lead to increased flow.
3

4. Medium Effects

The viscosity of the medium will of course affect the flow of fluid

through pinholes. Increasing viscosity will decrease the flow rate and thus

reduce the number of molecules of interest passing through the pinhole in a given time. If the medium swells the rubber then the pore size would be

expected to decrease slightly, decreasing flow. Otherwise, the chemical

constitution of the medium is expected to have little or no effect on flow

through pinholes.

5. Capillary Action or Wetting of Rubber

One could transport a fluid through a pinhole, and thus the particle in

the fluid, by capillary action. If one side of the condom is wetted by the

solution, the solution will be drawn by capillary action into and through the

rubber thereby wetting the other side of the condom. This mechanism will

certainly transport particles of a size smaller than the smallest pinhole in

the rubber. Often the condom comes packaged in lubricating oils or carrier

fluid. The properties of this additive will change the wetting characteristics

of the rubber membrane and thus effect the mechanism of capillary action

transport through the condom. We shall not model or discuss these mechanisms

further in this report.

6. Modeling of Flow Through a Pinhole as Capillary Flow

For lack of a better model on which to compute, we shall use the model of

flow in capillaries to describe the flow across membranes due to pinholes. The

flow through one capillary / is given by
4

Ji= 7T R/ Ap/(8 r, Li) ( 1 )

where is the flux in capillary i, Ap is the applied pressure, the length

of the capillary, its radius, and ij is the viscosity of the medium. Besides

assuming each pinhole is a capillary of cylindrical cross section, the above

equation assumes > R^ so that entrance effects are unimportant.

If we have a distribution of pinholes in a condom of uniform cross-section,

L, then the total flow, , is given by

where Jj is the total flow and the sum is over all pinholes in a condom. We

have assumed all lengths of capillaries are the same, L. A flux of for a time t leads to a volume Vp flowing through the membrane of

The above equations estimate steady state capillary flow. We have a substance

with concentration in the solution which is on the side of the membrane on which a pressure head has been applied. The solution on the other side of the

membrane, called the accepting solution, has a volume . The concentration of

the substance in the accepting solution, , after a volume flow of Vp is

Jj = n Ap/(8Lr7) R^^ ( 2 ) i

Vp=J^ t ( 3 )

Ca=Vf C,/(V^+Vp) ( 4 )

Since in all cases we will consider here V^^»Vp , we have
5

( 5 )

From equation 3 , 4 and 5 we have for the concentration in the accepting

solution as a function of time after some initial delay (called the

breakthrough time)

C^= C„ Ap t /(8 r, LV^ ) I ( 6 ) i

From equation 4 we can estimate the volume flow Vp from concentration

measurements on the accepting solution. If there is a single pinhole in the

membrane we can estimate the pinhole radius from this steady state flow .

where is the radius of the lone pinhole. If we have more than one pinhole

in the membrane, then all pinholes must have smaller radii than that estimated

from . Although the volume flow does not tell us pore size it allows us to

estimate the range of allowable pores. Equations 6 and 7 will be used later in our interpretation of the data.

We expect that there is an initial transient as the pinhole fills with

flowing solution. This transient is not easily estimated since it involves

wetting properties of the rubber, surface tension of the solution and entrance

effects in the capillary. Part of that transient will be the time to fill the

capillary by simply steady state flow. For a capillary i the time t^^^ can be

estimated as the time to fill the capillary by steady state flow. Since the

Rm‘= 8 C4

r, V* L/(* C„ Ap t) (7)
6

volume of capillary i is w L we have

7rRj^^L=7rApRi^tjji/(8r7L) (8)

Solving for the estimated breakthrough time we have

tbi= 8 n /Ap (L/Ri)2 (9)

Thus, the total volume , including the initial transient to fill the

capillary at the time t in steady state flow is given by

Vt=Vp - IT X Ri^ L (10)

i

Generally, for times over a few minutes the second term on the rhs of equation

10 is small. To estimate the order of magnitude of flows expected from our

experiment and from other tests for pinholes, we use the set of parameters

given in table 1.

We have estimated the values in table 1 in the following way; L is the

smallest value for thickness of condoms allowed by ASTM D3492^ ; rj is the

viscosity of water at room temperature; is the concentration of uranine

inside the condom in our experimental set up (see discussion below and in

appendix B) ; is the volume of buffer solution outside the condom (see

discussion of experiment setup below and in appendix A) ; Ap is the estimated
7

pressure head on the condom membrane, A is the approximate surface area of the

condom and is obtained assuming the condom is 180 mm long and 52 mm wide.^

From the parameters in table 1 we compute the transient time we estimated

in equation 9. Table 2 gives the estimated breakthrough times for these

parameters for pinholes of various radii. From this table the breakthrough

times estimated from just the steady state flow to fill up the capillary are insignificant compared to any time to be considered in this measurement. Thus

they may be disregarded. Furthermore, it is likely that this estimation of the

breakthrough time is only a minor component of the total breakthrough time for

pinhole flow through a capillary.

Let us assume that the condom has a single pinhole. We can estimate the

size of a single pore that can be measured by our method. If the flux through

the membrane of a small molecule like a fluorescence probe dissolved in water

is a result of pinhole flow then the equations above tell us of the

concentration change. On the other hand, if we can measure a given

concentration change then we can estimate the minimum detectible flow.

Equation 7 immediately tells us the radius of the pinhole that could cause that

flow if there is one pinhole and it is cylindrical.

We note below and in appendix B that we can detect as little as l.xlO"^

molar in uranine concentration in the accepting solution. We have by

rearranging equation 5

Vf=Ca Va/C, (11)

where as before Vp is the volume that flowed, is the concentration measured

in the accepting solution, is the volume in the accepting solution and is
8

the concentration in the flowing solution. Since we use a concentration of

10’^ molar in the flowing solution of the condom in our experimental setup and

the volume in the accepting solution inside the condom is about 250 mL we

estimate from eq. 11 that a Vj. as small as 2.5x10"^ mL can be measured.

We estimate the radius of the smallest single pinhole we can see by using

equation 1 and 3

R"= 8 Vj. r; Ap t^) (12)

where all terms have been defined before except tg which is the time in seconds

of the measurement.

Assuming the constants in table 1 we have for the radius of a single

capillary in the condom

r*=10-12 (13)

where tg is the flow time in seconds. Our flow times can easily exceed 40

hours (tg of 1.4x10^ seconds) which corresponds to detecting a single pinhole

of .5x10"^ cm (or .5 /im) radius. Of course, this flow could just as well have

come from 10,000 pinholes of .05 urn. Finally, we ask what size pinhole can be detected by a method like that

described in the section on leakage in ASTM Method D3492^ . The following

calculation is made on flow considerations only. Surface tension effects at

the air-water interface for a liquid passing through a small hole may be a more

significant factor in determining the minimum hole radius measurable by a technique like the leak test described in ASTM Method D3492. Thus the
9

following calculation may be viewed as a lower bound to the minimum radius

which can be measured by the ASTM method.

We shall assume the values of Ap, ri and L given in table 1. We assume

we can detect a droplet of 1.0 mm^ ( Vp=10"^ mL) and that there is no

evaporation of the droplet which would decrease its size. In a correct

treatment we would have to balance evaporation rate and spreading or wetting

rate with the flux through the pinhole to get a good estimate of the overall

rate. As these effects are difficult to treat we select a short flow time to

minimize their importance. A time of 30 seconds for the droplet to form (to=30

s) was selected. We find that the ASTM method can detect a pinhole of radius 6 micrometers. From the point view of flow considerations only our method is

about ten times more sensitive than the ASTM method.

B. Flow by Diffusion through the Membrane.

Even if there are no pinholes in the rubber, particles could pass through

the membrane by diffusion. This is a much slower process than pinhole flow,

however, since the whole membrane is available to diffusion, the total flux

from diffusion can be high. We shall discuss the properties of the rubber and

the flowing medium and how they affect diffusion before we consider modeling

the diffusion process.

1. Particle Size

In general, the larger the diffusing particle the smaller the flux from

diffusion. The Stokes-Einstein® relation suggests that the diffusion constant

and thus the flux of a diffusing particle is inversely proportional to the

radius of the molecule.
10

2o Medium Effects

The diffusion depends strongly on the state of the rubber, its thickness

and density variation. For example, the diffusion is faster in low density

regions. Medium effects on diffusion can be significant as well. For example,

the medium may swell the rubber causing an order of magnitude increase in the

diffusion coefficient of the diffusing particle.

3. Modeling of Flow through a Membrane Arising from Diffusion

Modeling of diffusion for this system is described by the diffusion

through a plane sheet. Although the condom is not a plane sheet the radius of

curvature of it is so large that the difference between a more correct

representation and a plane sheet insignificant. The mathematics and models have

been described in detail by Crank^ . His equation 4.24a best describes our

situation. This equation is

Qt/LCi=Dt/L2-l/6-2/?r2 exp (

- Dn^ t/L^ ) (14)

n

where is the total mass of diffusing species per unit area from the membrane

and, D is the diffusion constant of the species through the membrane in cm^ per

second. All other quantities have been defined previously except which is

the concentration of diffusant in the membrane on the side of the membrane

facing Cq which is in equilibrium with . In general, the relation between

and Cq is

Ci=KC, (15)
11

where K is the partition coefficient. Equations 14 and 15 lead to figure 1.

The dashed line in figure 1 is the asymptotic line given by

Qt=DKC„t/L-LKC^/6 (16)

while the intercept on the time axis is given by

ti„= LV(6D) (17)

t^j^ is called the breakthrough time since it estimates the time for some small

amount of material to appear on the other side of the membrane.

The total mass of uranine out of the condom in time t is where A is

the area of the condom. Thus, the concentration increase in the accepting

solution is

CA=QtAAA (18)

where again we have assumed the volume of the accepting solution is essentially

unchanged by the mass diffusing into it. For times much longer than the

breakthrough time we have from equation 16 and 18

C^/C,=DtKA/(V^L) (19)
12

For comparison purposes we need an estimate of the diffusion constants

and partition coefficients of molecules in rubber. In table 3 we list some

literature values of diffusion constants of small molecules in rubbers. These

range from 10"® to 10" ® cm^/s.

From the above equations and table 1 we can estimate what diffusion and

partition coefficients can be measured using our experimental setup.

Breakthrough times, tj^^^ , of 1/2 hour to 40 hours can easily be measured by our

technique. Thus, diffusion constants greater than 1 . 0x10" ^

^ cm^ /s can be

observed. We expect to be able to measure changes as small as C^/Cg of 2x10"®

in uranine concentration in 40 hours and products of KD greater than .5x10"^®

cm^ /s

C. Interpretation of Models of Flow

From the above discussion, it is clear that one cannot distinguish

between flow of small molecules across a membrane arising from pinholes in the

membrane or by diffusion of the molecules through the membrane. In both cases

we expect an initial delay time followed by a period during which the flux is

linear in time.

Ill Experimental

Since any measure of the number of molecules through a membrane depends

on the sensitivity of the method used to detect the species, we have chosen a fluorescence method since (1) it is extremely sensitive (for example, the

fluorescence compound we have chosen for our preliminary experiments, uranine,

may be detected in concentrations as low as one part per billion) and (2)
13

biological molecules with protein- like outer surfaces similar to the outer

surfaces of viruses can be labeled with fluorescent molecules.

Apparatus development and the preliminary experiments have been done

using uranine, the water soluble form of fluorescein, as the diffusing

molecule. This molecule is relatively small. It has a high fluorescence

intensity and is easily attached to a number of biological molecules. If

uranine is used as a tag of biological molecules it is important to have the

diffusion properties of the free molecules through the condom as baseline data.

The present measurements of the flux of uranine through a condom could act as preliminary data to that end. Otherwise, it serves as a measure of the volume

flow through pinholes or as a way to estimate the diffusion constants of larger

molecules

A sodium phosphate buffer solution of pH 7 was chosen as the medium for

the experiment.

A test apparatus was constructed with the following

considerations: 1) The condom should be expanded to around 300 mL. This

constraint is in concert with the filling volume used in the ASTM Method^ . 2)

The apparatus should exert no excessive stresses on the condom. 3) As much of

the surface of the condom should be tested as possible. 4) The volume of the

outer solution should be as low as can conveniently be stirred. (This allows

us to achieve high sensitivity. 5) Test conditions should be maintained for

at least 20 hours. A detailed description of the apparatus is given in

appendix A.

Large pinholes, those which do not allow us to keep a head of water in the

condom for even a few minutes, were a source of problems during the apparatus

development. Most large pinholes have been found near the rim of the opened
14

condom. Large pinholes near the rim of the condom are allowed by the ASTM

Method D3492^ . A method has been designed to pretest the condoms for large

pinholes before they are put on the test apparatus since large pinholes in the

body of the condom or close to the rim did not allow the apparatus to obtain a steady head of water.

Three different brands of condoms were tested. Measurments were made on four or five condoms of each brand. One of the three brands showed significant

differences from the other two. We shall discuss the data on all three

brands

A. Data on Brand B2

Experiments were made on condoms of type B2 . Condoms designated B2B, B2D

and B2E allowed little or no uranine to pass through the condoms in 20 hours

although we did see a fluorescence background increase. The fluorescence

spectra of the outer solutions of condom B2E is shown in figure 2. The reader

should notice the spectra is different from the spectrum of uranine of 10'®

molar shown on the same plot. Blank experiments with buffer alone indicated

almost no background increase in the fluorescence.

In one condom, B2C, we found a significant increase in the fluorescence

spectrum in the outer solution well above the background measured in any of the

other samples or in the blank. The outer solution had a concentration of

uranine of more than 2x10'® molar after 20 hours. Since the fluorescence

spectrum of this outer solution is very close to that of uranine, we conclude

that the concentration of uranine is greater than 1 ppb in the outer solution.

Since the first two hours of the run showed no fluorescence increase we are confident that the fluorescence observed in the outer solution is not due to
15

contamination . The spectra of the outer solution at various times up to 20

hours for condom B2C is given in figure 3. The plot of the concentration (in

the outer solution) versus time is given in figure 4. The data roughly showed

the expected breakthrough curve for molecules passing membranes with a breakthrough time for this data at about 3 -or 4 hours

B. Data on Brand B1

In experiments on condoms of type B1 we found that little or no uranine

passed through the condoms in the first 6 hours although we did see a fluorescence background increase. Measurements at 60 and 96 hours showed

uranine breakthrough the membrane. Blank experiments with buffer alone

indicated almost no background increase in the fluorescence.

Since the fluorescence spectrum of this outer solution is very close to

that of uranine for the 60 and 96 hour measurements, we conclude that the

concentrations of uranine are greater than 1 ppb in the outer solution. Since

the first six hours of the run showed no fluorescence increase we are confident

that the fluorescence is due to neither contamination nor a large pinhole.

Figure 5 shows the spectra of each condom of the B1 type at 96 hours.

Intensity data for the peak at 514 nm up to 96 hours for all condoms of this

type given in figure 6. The data roughly showed the expected breakthrough

curve for molecules passing through membranes with a breakthrough time of about

48 hours for all four condoms. The slope on the linear portion differ by a factor of two for this set of condoms. ' The highest slope BIB has a value of

2.2 I/s where I is the fluorescence intensity in arbitrary units at 515 nm

resulting from 490 nm excitation.
16

C. Data on B3

Experiments on condoms of type B3 showed this condom to be qualitativly

different from the other two brands tested. Within 1 hour of the start of the

experiment uranine in concentrations greater the 1.0x10"® molar had passed

through the condoms . Measurements were taken up to 20 hours . Blank

experiments with buffer alone indicated as shown in figure 7 almost no

background increase in the fluorescence. This figure should be compared with

the extremes of performance given in figure 8 of B3D which showed the lowest

concentration after 20 hours and figure 9 of B3B which shows the greatest

concentration in the outer solution after 20 hours. Plots of these data are given in figure 10 which shpw normal breakthrough curves with breakthrough

times of less then 1 hour. Slopes for the linear portion of the curves range

from S=140 I/s for B3B to S=2.4 I/s for B3D. Although the slopes are very

different if we rescale all the data so they are all normalized against their

concentration at 20 hours, the functional dependence of all four condoms look

remarkably similar (see figure 11) . This suggests that the condoms are

experiencing similar breakthrough times.

D. Comments on experiments

These preliminary experiments indicate that a valid method has been

developed which can be used to measure the rate at which molecules pass through

the condoms. The method should be useful on other condoms and may be

useful for determining the rates of passage of larger biological molecules.
17

From the above preliminary data on the condoms we draw some conclusions

about the nature of the flow through the condoms that we have tested. As

discussed in earlier sections the concentration of uranine in the outer

solution can be estimated for both diffusion and flow through a capillary

mechanism of mass transport through the condom membrane. From the description

above both pinhole and diffusive flow will show essentially the same

concentration versus time behavior. Equation 6 describes the concentration

increase in the accepting solution (or outer solution) in the case of a flow

through pinholes and equations 16-19 describe the concentration increase in the

accepting solution (or outer solution) in the case of diffusive flow of the

uranine through the membrane. In table 4, we collect together the data from

the three runs described above for estimated breakthrough times and slopes on

the linear portion of the concentration versus time plot. For diffusion there

is a known relation between the breakthrough time and the slope of the long

time portion of the curve through the diffusion constant and the partition

coefficient. In table 5, we give the estimated diffusion constants and

partition coefficients using ail method with our numbers. The data seem

inconsistent. For example, B3B and BSD have very different partition

coefficients. However, considering the experimental errors and the assumptions

made in analyzing the data the data are surprisingly consistent.

The diffusion constants obtained in table 5 are small when compared with

those of organics in rubber. However, uranine maybe charged in this highly

polar medium. We have noticed that the condoms are translucent when first put

into the buffer and become white after about 1 hour in the buffer solution.

This suggests that the condoms are taking up water. The diffusion constant of
18

water in rubber decreases with increasing water concentration® . Perhaps this

water also reduces the diffusion rate of uranine in rubber. This low diffusion

constant and the clouding of the condom indicates more studies on the effect of

the medium on the state of the condom are needed.

We may also estimate the flux of solution for pinhole flow through the

condom. Assuming the condom has only one pinhole, we may also estimate the

pinhole size. For this we use equation 7. The maximum pinhole that the

condom can have with this flux is given in table 6 for the data given in

table 4.

The data suggest flows from pinholes of about 1 micrometer. As we

pointed out before, these results may result from many more and much smaller

holes. These measurements have no way to distinguish between the two cases.

An apparatus for the measurement of flux of molecules through whole

condoms has been developed. It is shown that the experiment can measure

diffusion constants as low as 10"^® cm^/s or a single pinhole as small as .4

micrometer in the condom. On the basis of flow considerations only, the size

of pinholes measured by this technique is a factor of 10 smaller than that

detectible by current ASTM testing methods. Three different brands of condoms

were tested with the apparatus. Preliminary experiments suggest at least one brand had significant flux through the condom. Other brands had smaller but

measurable fluxes. Effects of the character of the medium have been noted.

Further experiments are necessary to distinguish between large holes and small

holes and fluxes due to diffusion and those due to pinholes. These results
19

suggest a more careful study of fluxes through condoms is necessary to assure

that a particle of diameter .1 micrometer cannot pass through the condom.
20

Table 1

L = 0 . 03 mm

rj - 0.001 Pa • s

Cq=. 001 molar=.3 g/L=.0003 g/mL

V^=250 mL

Ap=2xl0^ Pa

A=18500 mm^
21

Table 2

Estimate Breakthrough Times from Solution Flow Only for

Different Radius of the Capillary

Radius capillary (cm) Time(s)

3x10'

4.0x10-2

3x10- 4.0x10-'*

3x10-3 4.0x10-3
22

Table 3

Diffusion Constants and Partition Coefficients of Some

Small Molecules in Latex Rubbers+

D cm^/s

10®

O2 1.7

C2H2 .6

n-C,Hio .14

n-C5Hi2 .17

+ G. J. Van Amergon, Rubber Reviews, 37.> 1063, (1961).
23

Table 4

Data for Various Condoms

Condom

Approximate

Breakthrough time

Approximate

slope

s I/s C/s 10^5

(molar/s)

BIB 1.6x105 2.2 1.8

BID 1.7x105 1.1 .91

B3B > 1800 140 97

B3D > 3600 1.9 1.3

B2C 7.2x105 .58 .44
24

Table 5

Estimated Diffusion Constants (D) and Partition Constants (K)

Approximate D Approximate KD Approximate K

Condom from Breakthrough time from slope

cm^ /s cm^ /s

xlO^o xlO^°

BIB .09 oo .05

BID .09 3.2 .02

B3B >8.3 430 .02

B3D >74.1 7.7 .001

B2C 2 1.2 .001
25

Table 6

Estimated Maximum Possible Pinhole Size in Condom'*’

Condom Estimated Pinhole size in micrometers

BIB 1.1

BID .96

B3B 3.11

BSD .11

B2C .81

^Notice the results in this table are very model dependent. The model

assumes that flow comes from a single pinhole showing Pouisiiie flow throughout

the thickness of the condom. No diffusive flow is allowed. All modifications

of the model are expected to predict smaller pinholes.
26

References

1. L.S. Kish, J.T. McMahon, W. F. Bergfeld, and J.M. Pelachyk, Journ Am. Acad.

Dermatology. 9 . p 769-770 (1983).

2. Lee Schroeder , F. D . A. Private communication.

3. C.M. Guttman and E.A. DiMarzio, Macromoiecules , i31, (1970).

4. P. Heimetz, "Polymer Chemistry”, Marcel Dekker, N.Y. , 1984 pg. 601.

5. ASTM Standard Specification D3492-83, 1985 Annual Book of ASTM Standards,

Volume 09.02, pg. 449, ASTM, Philadelphia.

6. S. Glasstone, "Physical Chemistry", second edition, Macmiilian , London,

i960, pg. 261.

7. J. Crank, "The Mathematics of Diffusion", second edition, Oxford University

Press, 1975, London.

8. A.G. Thomas, and K. Muniandy, Polymer, 2^, 408, (1987).
27

CAPTION

Figure 1. Plot of mass of material, , as a function of time for diffusion

flow. A plot of similar functional form is expected from flow through a pinhole

Figure 2 Fluorescence emission spectra from condom B2E. Each solid line is at

a later time the lowest solid line being at 2 hours, the next three at 1 hour

intervals. The last line is the emission spectra at 20 hours. Dashed line is

1.0x10"® M uranine. Notice even the 20 hour spectra does not look like uranine

,

Figure 3. Fluorescence emission spectra from condom B2C. Each solid line is

at a later time, the lowest solid line being at 2 hours, the next three at 1 hour intervals. The last emission spectra is at 20 hours. Dashed line is

1.0x10"® M uranine. Notice ail the later spectra look like uranine.

Figure 4. Intensity of uranine that has flowed through a condom designated as B2C . For the conditions stated (excitation and emission wavelengths) an

intensity of about 1.4x10'^^ counts per second is equivalent to a concentration

of uranine of 1.0x10"® M. The curve has normal breakthrough behavior with a breakthrough time of about 2 to 4 hours. The estimated slope for the linear

portion S=,58 in units of I/s.

Figure 5. Fluorescence emission spectra BlA to BIE at 96 hours. Each solid

line is at a different condom. The lowest solid line is the blank BlA and is at
28

the baseline. Dashed line is 1.0x10"® M uranine. Notice all the spectra

except the blank look like uranine.

Figure 6. Intensity of uranine that has flowed through a condoms designated as

B1 . BIA is the blank, no uranine solution in the condom. All the rest have

uranine of concentration in the condom as explained in text. For the

conditions stated (excitation and emission wavelengths) an intensity’ of about

1.4 X 10^ counts per second is equivalent to a concentration of uranine of 1.0

X 10“ ® molar. All the condoms here show similar breakthrough times of 48 hours

and slope differences of about a factor of 2 on the linear portions. The

slopes range from 2.2 I/s for BIB to 1.0. I/s for BID.

Figure 7. Fluorescence emission spectra from condom B3A, the blank run for the

B3 series. Each solid line is at a later time, the lowest solid line being at

1 hours, the next three at 1 hour intervals. Dashed line is 1.0x10"® M uranine.

Figure 8. Fluorescence emission spectra from condom B3D. Each solid line is

at a later time, the lowest solid line being at 1 hours, the next three at 1 hour intervals. Dashed line is 1.0x10“® M uranine. Notice all the spectra

from the condom solutions look like the urnaine spectra.

Figure 9. Fluorescence emission spectra from condom B3B. Each solid line is

at a later time, the lowest solid line being at 1 hours, the next three at 1 hour intervals. Dashed line is 1.0x10"® M uranine. Notice all the later spectra

look like urnaine.
29

Figure 10. Intensity of uranine that has flowed through condoms designated as

B3 . B3A is the blank, no uranine solution in the condom. All the rest have

uranine of concentration in the condom as explained in text. For the

conditions stated (excitation and emission wavelengths) an intensity of about

1.4 X 10^ is equivalent to a concentration of uranine of 1.0 x 10~®M. These

condoms were very different than the rest. On this plot all of the condoms

show similar breakthrough times but have large slope differences.

Figure 11. Same data as in figure 10 but all data is rescaled so all

concentrations after 6 hours are the same. In this plot the data from the flow

through all the condoms of type B3 indicate similar breakthrough times of 2

hours or less.
30

Appendix A

Detailed description of the test apparatus.

In constructing a test apparatus, the following items were considered:

1. The condom should be expanded to around 250 mL.

2. Fluorophore used to detect breakthrough time should be soluble in pH 7 sodium phosphate buffer.

3. The volume of the outer solution should be as low as can conveniently be

stirred.

4. Test conditions should be maintained for at least 20 hours.

A single brand (Bl) was selected for trials until a reliable test

procedure was worked out.

The sample was suspended by stretching the open end over the lip of an inverted 35/20 borosiiicate glass socket. A 59 mm ID round-bottom borosilicate

glass tube served as immersion container. Prior to immersion and filling of

the condom with fluorescent (dye) solution, the container held a 4 mm OD

borosilicate glass sampling tube, a Teflon spinbar and 250-270 mL. buffer. In

initial experiments, expansion pressure was achieved by adding excess dye

solution to a height at 12 cm above the outer liquid level. Dye leakage at the

line of attachment was observed. Therefore, a pneumatic expansion of the

rubber was adopted, allowing excess dye solution to rise in an open-ended

vertical tube. Pressure was maintained by means of an adjustable bubbler

manostat with a flow rate just sufficient to make up for any gas leakage. By

adjusting dye solution volume and manostat, the liquid levels of inner and

outer solutions were equalized. This facilitated calculation of the inner

volume by displacement. Volumes of 250-260 mL at 12 cm H2 O pressure were
31

typical. At constant flow rate and fixed manostat setting, a subsequent rise

in the outer volume level was found to be caused by large pinholes. This was verified by forcing dye solution through the condom until droplets emerged.

The current design of the apparatus allows five tests be run

simultaneously on the same manostat.

In some instances we found that after 8 hours or so the volume of the

condom changed. As a result, we adjust the pressure head slightly to return

the volume of the condom to its original value.

It should be noted that upon immersion in the buffer or solution, all the

condoms appeared translucent. Within an hour or so all of them were opaque

(white). This may indicate that the condoms absorbed water.
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A
Figure 1

DIFFUSION IN A PLANE SHEET

Dt/L2
500

525

550

Wavelength

(nm)

Intensity

ro

b)

cn

X

o o

B2E:

1,

2,

3,

4,

20

Hours: X

=

490

NM

10'^M

Uranine/Buffer:

X

=

490

NM
500

525

550

Wavelength

(nm)

Intensity

ro

b)

cn

X

B2C:

1,

2,

3,

4,

20

Hours: X

=

490

NM

10'®M

Uranine/Buffer:

X

=

490

NM
Intensity o

cnooo oooo

cnooo

ro ro o cn o o o o o o

30000
500

525

550

Wavelength

(nm)

Intensity

CO

CO

X

o

>

otn

I

II

1 X 1 1

B1

(A,

B,

C,

D,

E):

96

Hours: X

=

490

NM

10

®M

Uranine/Buffer:

X

=

490

NM
Elapsed

Time

(Hours)

Intensity

Id

roocn

m o w

EXC

=

490

NM,

EMI

=

515

NM
Wavelength

(nm)

Intensity

X

I 1 1

B3A

(Blank):

1,

2,

3,

4

Hours: X

=

490

NM

10

®M

Uranine/Buffer:

EXC

=

490

NM
500

525

550

Wavelength

(nm)

Intensity

Ca}

o

X

B3D:

1,

2,

3,

4

Hours:

EXC

=

490

NM

10'^M

Uranine/Buffer:

EXC

=

490

NM
500

525

550

Wavelength

(nm)

Intensity

00

cn

X

o o

O)

T1H*

OQc

ro

B3B:

1,

2,

3,

4

Hours:

EXC

=

490

NM

10

®M

Uranine/Buffer:

EXC

=

490

NM
Elapsed

Time

(Hours)

Intensity

ro

-N|

00

X

o

EXC

=

490

NM,

EMI

=

515

NM
Intensity

o o

Figure

11
U.S. DEPT. OF COMM. 1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

BIBLIOGRAPHIC DATA

SHEET (See instructions) NBSIR 88-3721 APRIL 1988

4. TITLE AND SUBTITLE

"Flow of Molecules Through Condoms"

5. AUTHOR(S)

Charles M. Guttman

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Con tract/ Gremt No. NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

FDA 224-79-5023, Mod 16

t. Type of Report & Period Covered

Final Report

March 1 to May 1, 1987

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Food & Drug Admins itrat ion

Office of Science & Technology

12000 Wilkins Avenue

Rockville, MD 20852

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bliography or literature survey, mention it here)

An apparatus for the measurement of flux of small molecules through whole

condoms has been developed. It is shown that the experiment can measure diffusion

constants as low as 10~13 cm2/s or a single pinhole as small as .4 micrometers in

the condom. For pinhole measurements this is shown to be a factor of 10 better than

current ASTM testing methods on the basis of flow considerations only. Analysis of

the experimental data show the difficulties in making unambiguous determinations on

the mechanisms of flow. Further experiments are necessary to distinguish between

large holes and small holes and fluxes due to diffusion and those due to pinholes.

These results suggest a more careful study of fluxes through condoms is necessary

to assure that a particle about .1 micrometer cannot pass through the condom.

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) condom; latex condom; pinhole; diffusion

13. AVAILABILITY

I ^ I Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

14. NO. OF

PRINTED PAGES

46

15. Price

( ^ Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $11.95

uscomm*oc e04S>PB0

i