AuNPs／PNIPAM复合颗粒的制备及其温敏性质

将金纳米颗粒(AuNPs)组装到聚N-异丙基丙烯酰胺(PNIPAM)水凝胶微球表面制备出AuNPs/PNIPAM复合颗粒.将PNIPAM凝胶的温敏特性与AuNPs的光学性质结合,通过改变温度调节AuNPs的局部表面等离子共振(LSPR)吸收峰位置.研究结果表明,温度升高使AuNPs的LSPR吸收峰发生红移,并且这种效应是可逆的.同时发现,AuNPs的光学性质还可以作为表征PNIPAM水凝胶微球温敏行为的一种手段.利用透射电镜、紫外-可见光谱仪及动态光散射仪对AuNPs/PNIPAM复合颗粒的形貌、光学性质、粒径变化等进行了分析.

P(NIPAM-NVP)温敏凝胶膜的制备及其性质研究

制备了N-乙烯基吡咯烷酮(NIPAM)改性的聚异丙基丙烯酰胺凝胶膜,分别研究了NIPAM和交联率对凝胶的平衡含水率和扩散行为的影响。结果表明:NIPAM的加入以及凝胶交联率的降低,皆可导致凝胶平衡含水率的提高。水分子在凝胶中的扩散行为属非Fick扩散,并且随着NIPAM的加入以及凝胶交联率的降低,扩散特征指数和扩散系数增加。

Molecular chain properties of poly(N-isopropyl acrylamide)

A series of poly（ N-isopropyl acrylamide） （PNIPAM） samples with molecular weight ranging from 2.23×104 to 130×104 and molecular weight distribution Mw/Mn≤1.28 were obtained by free radical polymerization and repeat precipitation fractionation. The molecular weight Mw, second virial coefficient A2 as well as the mean-square-root radius of gyration 〈S2〉 for PNIPAM samples in tetrahydrofuran （THF） were determined by light scattering, and the relations were estimated at A2 ∞ Mw0.25) and 〈S2〉1/2=1.56×10-9 Mw0.56. The intrinsic viscosity for THF solution and methanol solution of PNIPAM samples was measured and the Mark-Houwink equations were obtained as [η]=6.90×10-5 M0/73 （THF solution） and [η]=1.07×10-4 M0.71 （methanol solution）. The above results indicate that both THF and methanol are good solvents for PNIPAM. The limit characteristic ratio C∞ for PNIPAM in the two solutions was determined to be 10.6 by using Kurata-Stockmayer equation, indicating that the

Thermal reversible gelation during phase separation of poly(N-isopropyl acrylamide)/water solution

By dynamic viscoelastic measurement for PNIPAM/water solution it has been found that below the phase separation temperature (about 32 ℃), the system is homogeneous fluid; while upon being heated to about 32 ℃, the solution undergoes phase separation and the storage modulus G’ increases sharply and exceeds the loss modulus G', indicating the physical network formation during the phase separation. Based on the percolation model, the gel points Tgel, were obtained by applying the dynamic scaling theory (DST) and winter’s criterion. The critical exponent n was also obtained to be 0.79 through DST, which is different from 0.67, the critical point of chemically crosslinked network predicted through DST. The obtained n value reflects the special property of physical network being different from chemical network.

Novel Method to Monitor the De-Swelling of PNIPAAm Hydrogels of Different Cross-Link Density

The effect of cross-linker (methylene-bis-acrylamide) (MBA) on the volume phase transition, mechanical properties and de-swelling of Poly(N-isopropyl acrylamide-co-methylene-bis-acrylamide) hydrogel (PNIPAAm/MBA hydrogel) was investigated. A new method, namely isothermal thermo-gravimetry was developed for monitoring de-swelling of PNIPAAm/MBA hydrogel. Monomer/ Cross-linker ratio of the initial monomer composition R = moleNIPAAm/moleMBA was introduced. It has been proven earlier that initial monomer composition is close to the copolymer composition;hence R values may be used to express cross-link density. Hydrogels from R10 to R150 were investigated. The results of DSC analysis revealed that the less the cross-linker ratio in the gel (from R10 to R150) the more sharp the temperature range of volume phase transition and the higher its enthalpy. Cross-link density, namely increasing cross-linker content in the copolymer (R from 150 to 10) does not significantly affect the temperature range of volume phase transition. It sets on at 33°C - 34°C, and ends between 35?C and 38?C. Cross-link density has significant effect on compression modulus. By decreasing the ratio of cross-linker (by increasing R from 10 to 150), the compression modulus increases, goes through a maximum, and then decreases. The highest compression modulus was measured for PNIPAAm/MBA hydrogel R20. Hydrogels with cross-linker content between R100 and 30 are strong enough and have their thermoresponsivity. Isothermal thermograms of de-swelling are of similar character for all the gels with different cross-linker content. During the initial stage of de-swelling for gels with higher cross-linker content (R10 - R15) the solute release is quicker than for gels R20 - 150 and the thermograms are drawn out. In the initial stage of de-swelling, i.e. during the first 40 minutes the rate of solute release is the highest for gels R70 - 150. The cross-linker content effects solute release, especially for gels with high cross-linker content. It is noteworthy that gels R10 - 15 release solute quicker than gels R30 - 50 and their rate of de-swelling is comparable to that of gels R100 - 150. The novel thermogravimetric method enables the selection of gels based on the rate of solute release and it can also be applied for other cross-linked gels.

APPLICATION OF NONIONIC TEMPERATURE SENSITIVE HYDROGEL FOR CONCENTRATION OF PROTEIN AQUEOUS SOLUTION

Six different N-alkyl substituted acrylarnide nonionic hydrogels were prepared and their swelling characteristics were measured. Poly N-isopropyl acrylamide (PNIPA) and poly N-n-propyl-acrylamide (PNNPA) temperature sensitive hydrogels were chosen as the nonionic temperature sensitive hydrogels for concentration of very dilute aqueous protein solution. The separation properties of PNIPA and PNNPA hydr0gels with different network dimensions were studied and the modification of the hydrogels was surveyed in order to decrease their surface adsorption of protein molecules. The experimental results of the concentration of BSA (Bovin serum albumin) dilute aqueous solution by hydroxylpropyl methacrylate (HPMA) copolymerized PNIPA hydrogel were given. The value and the limitation of concentration of dilute aqueous protein solution by this method was evaluated.