Flow cell and method for continuously monitoring deposits on flow surfaces

A demountable, rectangular, liquid sample flow cell is provided which can be used to make streaming potential or streaming current measurements from which the zeta potential is calculated. By providing an infrared transparent window in the flow cell, a real-time monitoring of surface deposition rates and amounts can be determined by infrared radiometry. Because the flow cell is completely demountable, direct analysis of the internal surfaces exposed to the flowing solution is possible.

There are a number of situations in which a surface is subject to being 
coated with biological films as from biological fouling in the case of sea 
water and from adsorption of blood proteins in the case of in vivo 
implants. The characterization of several surfaces exposed to various 
blood proteins requires information on the zeta potential of the material 
making up the surfaces. Basically, two techniqes are available for this 
determination. First, using the mobility of particles in an electric 
field, it is possible to make electrophoretic measurements on small 
(2.mu.dia.) particles from which their zeta potential can be determined. 
The second technique involves flowing a solution through a circular 
capillary made of the material of interest. Neither of these techniques 
lends itself to an examination of the surface nor are they suitable for 
the complete list of electrical measurements to be made or for a measure 
of the conformation of the adsorbed protein. If, as in the case of blood 
proteins, the solution contains adsorbable species, then the adsorbed film 
thickness, molecular conformation and its wettability could not be 
obtained using small particles or a capillary of the material. 
Microfouling of solid surfaces by spontaneously adsorbed films and then by 
biological slimes has important efficiency-limiting effects on heat 
exchangers, and predisposes the surfaces to thicker macrofouling deposits 
(see Reference). Specific surface properties of the materials (chemical, 
electrical, textural) strongly influence the nature of the first acquired 
films, their subsequent resistance to shear-induced detachment and/or 
cleaning, and their immobilization of boundary liquid layers. The flow 
cell of the present invention permits a determination at controlled shear 
rates of the following parameters of the spontaneously adsorbed film: 
change in streaming (and zeta) potentials; rest potentials; contact 
potentials; infrared spectra of the initial deposits; film thicknesses and 
refractive indices; change in critical surface tension; surface texture; 
and associated inorganic elements prior to mineralization. By providing a 
window transparent to infrared energy, radiometric measurements of heat 
transfer parameters in real time as well as values of streaming (and zeta) 
potentials at a variety of controlled shear rates and shear stresses are 
possible before, during and after the adsorption of biological films. This 
arrangement also allows the measurement of normal rest potential for 
metallic surfaces in equilibrium with their contacting electrolytes and 
modification of that potential in a "voltage clamping" arrangement in both 
static and flow experiments. By assembling the flow cell using two 
internal reflection plates separated by thin glass shims, substituting for 
the capillary geometry which is normally used for zeta potential 
measurements, the flow cell can be rapidly taken apart after each flow 
experiment for the measurement of the infrared absorbing properties, 
thickness, surface potential and structure of the adsorbed protein films. 
It is an object of this invention to provide a method and apparatus for the 
direct observation of the adsorption process in a protein media. 
It is a further object of this invention to provide a demountable flow cell 
suitable for use in making streaming potential measurements and for the 
direct analysis of the internal surfaces exposed to the flowing solution. 
It is an additional object of this invention to provide a readily 
disassembled flow cell. 
it is a still further object of this invention to provide a method and 
apparatus for the real-time monitoring of surface deposition rates and 
amounts by infrared radiometry. These objects, and others as will become 
apparent hereinafter, are accomplished by the present invention. 
Basically, a flow cell is provided which is held assembled in a fluid tight 
manner by a clamp structure. Where the sample contains an adsorbable 
species, it will be deposited onto the flow cell surfaces as the solution 
passes through the cell. By providing surfaces which are optical elements 
used for internal reflection infrared analysis of the adsorbed species as 
internal surfaces of the flow cell, measurement of the infrared absorbing 
properties, thickness, surface potential and structure of the adsorbed 
protein film can be monitored in real-time and measured upon disassembly 
of the flow cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1-3, the numeral 10 generally indicates a flow cell for 
use in measuring the adsorption of blood proteins. The flow path in the 
flow cell 10 is defined by germanium or germanium coated plates 12 and 14 
which are separated by glass shims 16 and 18. In an actual apparatus used, 
the n-type germanium plates 12 and 14 were 2.times.5.times.0.1 cm thick, 
the glass shims 16 and 18 were 0.5.times.5.times.0.015 cm thick and when 
assembled formed a 1.times.0.015 cm flow path through the device, but 
these dimensions are not critical. The plates 12 and 14 and shims 16 and 
18 are held together by housing members 20 and 22 and plates 12 and 14 are 
received in matching relieved areas in housing members 20 and 22. Flow 
line members 30 and 32 are received in matching relieved portions of 
housing members 20 and 22 and form a part of the flow path through the 
flow cell 10. Housing members 20 and 22 and thereby plates 12 and 14, 
shims 16 and 18, and flow line members 30 and 32 are held in a proper and 
fluid tight relationship by hose clamps, or like devices, 36 and 38. The 
flow cell 10 is readily taken part by removing hose clamps 36 and 38 and 
this permits the direct measuring of infrared absorbing properties, 
thickness, surface potential and structure of the adsorbed protein film 
which forms on the internal surfaces of flow cell 10 at the solid/liquid 
interface as a protein containing solution flows through the flow cell 10. 
Because germanium has excellent infrared transmission properties in the 
sensing range of existing infrared radiometers, the flow cell 10 of FIGS 
1-3 may be modified to flow cell 110 of FIGS. 4 and 5 by providing an 
optical path or window 121 through housing member 120 to germanium or 
germanium coated plate 112 in housing member 120 to permit real-time 
monitoring of surface deposition rates and amounts. Flow cell 110 is 
otherwise identical to flow cell 10 of FIGS. 1-3. 
OPERATION 
The operation of the flow cell 10 of FIGS. 1-3 is best understood with 
reference to FIG. 6. The protein-containing electrolyte flows in a fluid 
path between silver/silver chloride electrodes 40 and 42 via flow cell 10. 
Platinum ribbons 44 and 46 are provided to make electrical contact with 
germanium plates 12 and 14, respectively. A number of measurements may be 
made by varying the electrical connections and providing the proper 
instrumentation. In the arrangement illustrated, switch 50 is selectively 
movable to complete an electrical circuit containing electrodes 40 and 42 
for measuring streaming potential via differential voltmeter 52. In the 
other position of switch 50, electrode 42 and plate 14 are connected to 
digital voltmeter 56 via unity gain high impedance amplifier 54 for 
measuring the rest potential. 
The operation of the flow cell 110 of FIG. 4 is best understood with 
reference to FIG. 7 and is essentially the same as that of the flow cell 
10 of FIG. 6. In FIG. 7, structure corresponding to the structure of FIG. 
6 is numbered one hundred higher. Flow cell 110 is capable of permitting a 
real-time monitoring of the conditions within the flow cell through the 
use of infrared radiometer 150. Because germanium is infrared transparent 
in plates of relatively thin thicknesses, plate 112 is transparent to the 
infrared radiation detectable by infrared radiometer 150, and the interior 
of cell 110 is visible and available for real-time monitoring of surface 
deposition rates and amounts. 
Although preferred embodiments of the present invention have been 
illustrated and described, other changes will occur to those skilled in 
the art. For example, the flow cell members have been secured in a fluid 
tight relationship by end blocks including structure for receiving the 
electrodes. It is therefore intended that the scope of the present 
invention is to be limited only by the scope of the appended claims. 
REFERENCE 
V. A. DePalma and R. E. Baier, "Microfouling of Metallic and Coated 
Metallic Flow Surfaces in Model Heat Exchange Cells", a paper presented 
and passed out at the OTEC Conference in Seattle, October, 1977.