羟丙基甲基纤维素在不同界面的表面活性

Surface Activity of Hydroxypropyl Methylcellulose at Different Interfaces

在不同浓度和pH值下，考察了羟丙基甲基纤维素（HPMC）粉末在水表面的动态接触角以及HPMC溶液在气-液、油-水界面的表面张力．结果表明：HPMC粉末的润湿性不强，且受pH值的影响不大，当pH＝4．00时，接触角最低为86．380°；无论在气-液界面还是在油-水界面，表面张力主要取决于界面区域的HPMC 分子链构象变化，这与溶液pH值和溶液浓度有关；质量浓度为0．1％的HPMC溶液，气-液界面的表面张力随pH值增大而增大，质量浓度为0．3％～1．0％的HPMC溶液，气-液界面的表面张力随pH增大呈“∨”形变化，说明界面区域的HPMC分子链构象变化复杂；油-水界面的HPMC与界面上的油脂分子相互作用，使得HPMC分子链构象变化更为复杂；当pH≥6．00时，油-水界面的表面张力随pH值增大而减小，而在pH＜6．00时，浓度的影响更大，油-水界面的表面张力上下波动．

The dynamic contact angle of hydroxypropyl methylcellulose （HPMC）powders on water surface,as well as the air-water and the oil-water surface tensions of HPMC aqueous solution,were investigated at different concen-trations and pH values.The results show that （1 ）the wettability of HPMC powders is not strong enough and is slightly affected by the pH value;（2）the contact angle reaches its minimum 86.380°at pH 4.00;（3）the sur-face tension of HPMC aqueous solution mainly depends on the change of molecular chain conformation in the inter-facial area and varies with both the pH value and the concentration;（4 ）the air-water surface tension increases with the pH value at the mass concentration of 0.1%and shows a V-shaped variation with the pH value at the mass concentration ranging from 0.3%to 1 .0%,which illustrates the complex change of HPMC molecular chain confor-mation in the interfacial area;（5 ）the conformation of HPMC molecular chains becomes more complex at the oil-water interface due to the interaction between HPMC and the lipid in the oil;and （6）the oil-water surface tension decreases with the increase of pH value that is not less than 6.00,and varies irregularly due to the greater effect of concentration when the pH value is less than 6.00.