Patent Application: US-52470306-A

Abstract:
the compositions of hydrogel colloidal crystals are made from mixing an aqueous suspension of poly - n - isopropylacrylamide - co - allylamine microgels with dichloromethane , forming a pnipam - co - allylamine / dichloromethane mixture . the pnipam - co - allylamine / dichloromethane mixture is incubated for a period of time at a given temperature , forming the colloidal crystal material . the colloidal crystals can be stabilized by diffusing a glutaric dialdehyde solution into the colloidal crystal material . the concentration of polymer matrix microgels can determine the orientation of random or columnar crystals .

Description:
terms : it will be readily apparent to one skilled in the art that various substitutions and modifications may be made in the invention disclosed herein without departing from the scope and spirit of the invention . the term “ a ” or “ an ” as used herein in the specification may mean one or more . as used herein in the claim ( s ), when used in conjunction with the word “ comprising ”, the words “ a ” or “ an ” may mean one or more than one . as used herein “ another ” may mean at least a second or more . the term “ colloid gel ” as used herein includes a colloid in a more solid form than a sol . the term “ crystal ” as used herein includes a solidified form of a substance in which the atoms or molecules are arranged in a definite pattern that is repeated regularly in three dimensions : crystals tend to develop forms bounded by definitely oriented plane surfaces that are harmonious with their internal structures . the term “ hydrogel ” as used herein includes a colloidal gel in which water is the dispersion medium . the term “ columnar phase ” as used herein includes a liquid crystal phase characterized by disc - shaped molecules that tend to align themselves in vertical columns . the following examples are provided to further illustrate this invention and the manner in which it may be carried out . it will be understood , however , that the specific details given in the examples have been chosen for purposes of illustration only and not be construed as limiting the invention . the materials used to produce columnar microgel crystals are as follows : n - isopropylacrylamide ( nipam ) was purchased from polyscience co . and recrystallized from hexanes and dried in air prior to use . n , n ′- methylene - bis - acrylamide ( bio - rad co . ), potassium persulfate , sodium dodecyl sulfate , dichloromethane and allylamine ( aldrich ) were used as received . water for all reactions , solution preparation , and polymer purification was distilled and purified to a resistance of 18 . 2 mωcm using a millipore system , and filtered through a 0 . 22 μm filter to remove particulate matter . in one embodiment , the preparation of monodispersed poly - n - isopropylacrylamide ( pnipam )- co - allylamine colloidal spheres was as follows : monodispersed poly - n - isopropylacrylamide ( pnipam )- co - allylamine colloidal spheres were prepared using precipitation polymerization . [ 25 ] nipam monomer ( 3 . 8 g , 33 . 6 mmol ), allylamine ( 0 . 2 g , 3 . 4 mmol , 10 mol % of nipam monomer ), sodium dodecyl sulfate ( 0 . 08 g , 0 . 28 mmol ) and n , n ′- methylene - bis - acrylamide ( 0 . 067 g , 0 . 44 mmol , 1 . 3 mol % of nipam monomer ) in water ( 240 ml ) at room temperature were purged with nitrogen and stirred for 30 min , and then heated to 60 ° c . potassium persulfate ( 0 . 166 g ) in 10 ml water was added to the reactor to initialize polymerization . the reaction was maintained at 59 - 61 ° c . under nitrogen for 5 h . after cooling to room temperature , the resultant microgels were dialyzed for 2 weeks to remove surfactant and un - reacted molecules . the dialysis water was changed three times every day . the cutoff molecular weight of the dialysis membrane was 13 , 000 . after dialysis , pnipam - co - allylamine microgels were concentrated by ultra - centrifugation at 40 , 000 rpm for 2 hours and re - dispersed with di water to a certain concentration . the solid concentration of the suspension was obtained by completely drying at 80 ° c . in air and weighed . these particles showed the phase behavior similar to that of a pure pnipam gel [ 26 ] with a slightly higher volume phase transition temperature around 35 ° c . the average hydrodynamic radius of the particle was about 135 nm at 22 ° c . with polydispersity index ( pd . i ) about 1 . 08 and shrank to 65 nm at 37 ° c . with pd . i about 1 . 01 ( fig1 ). the pnipam - co - allylamine microgel columnar crystals were prepared by adjusting the centrifuged particle suspension to concentrations ranging from about 1 . 8 to about 4 . 5 wt %. the defined amounts of dichloromethane ( ch 2 cl 2 ) 0 . 27 g with 1 g particle suspension were mixed by shaking for two minutes . the mixture was put into an incubator . the crystal formation was observed at each temperature for several days . dynamic light scattering measurements : a commercial laser light scattering spectrometer ( alv , co ., germany ) was used with a helium - neon laser ( uniphase 1145p , output power of 22 mw and wavelength of 632 . 8 nm ) as the light source . the hydrodynamic radius distribution of the pnipam - co - allylamine microgels in water was measured at the scattering angle of 60 °. uv - visible spectroscopy measurements : the turbidity ( α ) of the gels was measured as a function of the wavelength using a diode array uv - visible spectrometer ( agilent 8453 ) by calculating the ratio of the transmitted light intensity ( i t ) to the incident intensity ( i o ) α =−( l / d ) ln ( i t / i 0 ) , where d is the thickness ( 1 mm ) of the sampling cuvet the growth of columnar microgel crystals and the kinetics of crystal growth was determined . an aqueous suspension of pnipam - co - allylamine microgels with polymer concentration 3 . 5 wt % was then mixed with dichloromethane by shaking at 22 ° c . all samples contain the microgels with the average hydrodynamic radius of 135 nm and have the same suspension to oil ratio of 1 : 0 . 27 . after homogenization , the mixture was left to stand . this initial mixture ( fig2 a ) appeared cloudy . the outside diameter of test tubes is 1 . 0 cm . within about 4 hours ( fig2 b ), small columnar crystals were observed growing from the top to the bottom , which was in contrast to the hard sphere system that grew from the bottom to the top . [ 2 ] the crystals grew longer with time along the direction of gravity and reached about 1 . 5 cm after 82 hours ( fig2 g ). the mixture can be generally divided into three portions : the top portion is the crystal phase , the bottom portion ( cloudy ) is un - emulsified organic solvent , and the middle portion is unstable water - oil emulsion ( cloudy and white ). although not wanting to be bound by theory , the mixture apparently formed an un - stable oil - in - water emulsion with “ micelles ” consisting of organic oil droplets coated by many microgels . this suggestion is not unreasonable when considering that the pniapm particles have been used as emulsifiers . [ 27 ] using an optical microscope , the sizes of the “ micelles ” were found to range from 10 to 40 μm ( fig3 ). as a note , there is not enough resolution in fig3 to see microgels in this optical microscopic picture . however , previous sem measurements supported that pnipam microgels can cover the surfaces of oil droplets . [ 27 ] because limited emulsifying ability of pnipam particles , un - emulsified oil quickly sink to form an oil phase in the bottom . these “ micelles ”, which are heavier than water due to higher mass density of organic solvent ( 1 . 33 g / ml ), gradually sink to the bottom of the cuvette . the mismatch of surface tension between particle - oil and the oil - water , results in coarsening . when such coarsening occurs , the microgels at the surface of the micelles are released . these released particles self - assemble into columnar crystals that originate in the interface between the mixture and air . the colors observed from columnar crystals are due to diffraction from the ordered colloidal arrays with a lattice spacing on the order of the wavelength of visible light according to the bragg &# 39 ; s law : 2ndsinθ = mλ , where n is the mean refractive index of the suspension , θis the diffraction angle , d is the lattice spacing , m is the diffraction order , and λis the wavelength of the diffracted light . [ 6 ] fig4 shows the uv - visible spectra at three locations of columnar crystals . the peak position shifts to shorter wavelengths from the top to the bottom part of the columnar crystals . this indicates that the interparticle spacing of the bottom is smaller than that of the top . in contrast , for randomly oriented crystals , prepared in pure water , the peak position does not change with the location in the crystals ( fig5 ). different morphologies of columnar colloidal crystals can be obtained by changing polymer concentration . for example , fig6 shows mixtures of the aqueous suspension of pnipam - co - allylamine microgels with dichloromethane at various pnipam polymer concentrations ranging from 1 . 8 to 4 . 5 wt % at 22 ° c . for samples below 2 . 0 wt % ( fig6 ( 1 - 2 )), no crystallization was observed . near 2 . 2 wt % ( fig6 ( 3 )), conventional , randomly oriented crystalline domains appeared . for samples near 2 . 5 wt % ( fig6 ( 4 )), there was a co - existent region of columnar crystals and conventional crystal domains . for samples with polymer concentration between 2 . 7 and 3 . 5 wt % ( fig6 ( 5 - 8 )), columnar crystals were observed . in this concentration range , the color of the columnar crystals changed from red to blue as polymer concentration increases . uv - visible spectra on these crystals at the same location also demonstrated that the peak position shifts to a shorter wavelength with the increase of the polymer concentration ( fig7 ), due to the decrease of inter - particle spacing . near 4 . 0 wt % ( fig6 ( 9 )), a co - existent region of columnar crystals and randomly oriented crystalline domains was observed . at 4 . 5 wt % ( fig6 ( 10 )), only randomly oriented crystalline domains were observed . additionally , the current method could be used to row randomly oriented crystalline domains at high polymer concentrations at room temperature , while the previous method relies on the heating - cooling cycles . [ 14 , 28 ] both temperature and polymer concentration have been utilized and measured for the formation of columnar crystals . fig8 shows a phase diagram of the mixtures of the aqueous suspension of pnipam - co - allylamine microgels with dichloromethane . the phase behavior has been divided into four areas : liquid , ( randomly oriented ) crystal , columnar crystal , and glass . the columnar crystals and randomly oriented crystals co - exist phases are indicated with thick blue lines . in the liquid phase region , the top portion of the mixture flows easily , while in the glass phase region it cannot flow . growth kinetics of columnar crystals depends strongly on temperature . at 22 ° c ., it took about two or three days for crystals to grow to 1 cm long . however , above 26 ° c ., no crystals were observed after seven days . stabilizing a columnar crystal structure can be achieved by bonding neighboring particles . the direct use of pnipam columnar colloidal crystals is limited because the structure can be easily destroyed by any external disturbance such as vibrations . to solve this problem , the stabilization of columnar crystalline hydrogels by bonding particles into a network has been used . monodispersed poly - n - isopropylacrylamide ( pnipam )- co - allylamine colloidal spheres were prepared using precipitation polymerization as described in example 2 . the centrifuged particle dispersion was adjusted to polymer concentration ranging from 3 . 5 wt % to 4 . 23 wt %. the defined amounts of dichloromethane ( ch 2 cl 2 ) 0 . 2 g with 1 g particle dispersion were mixed by a mixer for 2 minutes . the mixture was put into 23 ° c . incubator and the columnar crystals were formed in about 2 to 3 days . after the crystals were formed , the dispersion was put into an incubator with a temperature of 4 ° c . for about 24 hours . then glutaric dialdehyde ( 0 . 04 g , 25 wt .%) solution was added to the top of the dispersion . this reagent was diffused through the dispersion to act as cross - linker . the particle assembly with columnar crystalline structure was stabilized by the cross - linking reaction for about two days in incubator having a temperature of about 4 ° c . the cross - linked columnar crystal gel was removed from the test tube by injecting water into bottom of the tube with a syringe . after measured the turbidity by uvnis spectrophotometer ( agilent 8453 ) and the gel size , the gel was immersed in di water for 1 week to balance the gel . during the balancing period , the di water was changed three times every day to remove un - reacted glutaric dialdehyde . the anisotropic properties of hydrogels with columnar crystals was determined . conventional hydrogels swell or shrink isotropically . however , this isotropic symmetry is broken for hydrogels with columnar crystals . fig9 shows swelling behavior of the columnar crystal hydrogel with 4 . 23 wt % polymer concentration . fig9 a shows the hydrogel was just taken out from the test tube . after 5 days , the gel reached a fully swollen state ( fig9 b ). as one can see from the pictures , the gel swollen more along the direction that is perpendicular to the long axis of the columnar crystals than along the direction of the long axis . if we define the ratio of gel &# 39 ; s length ( l ) to diameter ( d ) as an anisotropic parameter . if this ratio is one , the gel swells isotropically . if this ratio is not equal to one , the gel swells anisotropically . it is found that for columnar crystal gels , the ratio of l / d is smaller than one and decreases from 0 . 95 to 0 . 89 as the polymer concentration decreases from 4 . 23 % to 3 . 5 % ( fig1 , blue line ). a controlled experiment showed that for randomly oriented crystalline hydrogels , this ratio of ( l / d ) is always equal to one ( fig1 , the dark line ). as an alternative , the formation of columnar crystal hydrogels , microgels can utilize : nipam co - polymerize with monomers that contain amine group , or carboxyl , or hydroxyl group such as allylamine , 2 - hydroxyethyl acrylate , 2 - aminoethyl methacrylate hydrochloride , n -( 3 - aminopropyl ) methacrylamide hydrochloride , acrylic acid , or any above two functional groups . additionally , alternative organic solvents include c n h ( 2n + 2 − y ) x y ( where x = f , cl , i , br and n = 1 , 2 , 3 . . . and y = 1 , 2 , 3 , . . . ) such as methane chloromethane , dichloromethane , chloroform , carbon tetrachloride , 1 , 2 - dichloroethane , etc . one skilled in the art readily appreciates that this invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned as well as those inherent therein . the compositions , methods , procedures and techniques described herein are presently representative of the preferred embodiments and are intended to be exemplary and are not intended as limitations of the scope . changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention or defined by the scope of the pending claims . the following references , to the extent that they provide exemplary procedural or other details supplementary to those set forth herein , are specifically incorporated herein by reference . u . s . patent application ser . no . 10 / 295 , 484 filed by hu et al ., on nov . 15 , 2001 and titled “ synthesis , uses and compositions of crystal hydrogels .” u . s . pat . no . 5 , 532 , 006 issued to lauterbur , et al ., on jul . 2 , 1996 , titled “ magnetic gels which change volume in response to voltage changes for mri .” u . s . pat . no . 5 , 976 , 648 issued to li , et al ., on nov . 2 , 1999 , titled “ synthesis and use of heterogeneous polymer gels .” u . s . pat . no . 5 , 062 , 841 issued to siegel on nov . 5 , 1991 , titled “ implantable , self - regulating mechanochemical insulin pump .” u . s . pat . no . 4 , 912 , 032 issued to hoffman , et al ., on mar . 27 , 1990 , titled “ methods for selectively reacting ligands immobilized within a temperature - sensitive polymer gel .” u . s . pat . no . 4 , 555 , 344 issued to cussler on nov . 26 , 1985 , and titled “ method of size - selective extraction from solutions .” k . e . davis , w . b . russel , w . j . glantschnig , science 1989 , 245 , 507 . b . j . ackerson , s . e . paulin , b . johnson , w . van megen , s . underwood , phys . rev . e , 1999 , 59 , 6903 . j . yamanaka , m . murai , y . iwayama , m . yonese , k . ito , t . sawada , j . am . chem . soc . 2004 , 126 , 7156 . p . jiang , j . f . bertone , k . s . hwang , v . l . colvin , chem . mater . 1999 , 11 , 2132 . m . weissman , h . b . sunkara , a . s . tse , s . a . asher , science 1996 , 274 , 959 . a . van blaaderen , r . ruel , p . wiltzius , nature 1997 , 385 , 321 . z . cheng , w . b . russel , p . m . chaikin , nature , 1999 , 401 , 893 . s . h . park , d . qin , y . xia , adv . mater . 1998 , 10 , 1028 . c . lellig , w . hartl , j . wagner , and r . hempelmann , angew . chem . int . ed . 2002 , 41 , 102 . j . d . debord , s . eustis , s . b . debord , m . t . lofye , l . a . lyon , adv . mater . 2002 , 14 , 658 . z . b . hu , x . lu , j . gao , adv . mater . 2001 , 13 , 1708 . s . j . tang , z . b . hu , z . d . cheng , j . z . wu , langmuir 2004 , 20 , 8858 . t . tanaka , i . nishio , s . t . sun , s . ueno - nishio , science 1982 , 218 , 467 . m . j . snowden , m . j . murray and b . z . chowdry , chemistry & amp ; 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