Wilder Elizabeth A, Hall Carol K, Spontak Richard J
Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695, USA.
J Colloid Interface Sci. 2003 Nov 15;267(2):509-18. doi: 10.1016/s0021-9797(03)00619-2.
The 1,3:2,4-dibenzylidene-D-sorbitol (DBS) molecule is capable of self-organizing into nanoscale fibrils through intermolecular forces such as hydrogen bonding and pi interactions. At sufficiently high concentrations (typically less than approximately 2 wt%), the nanofibrils can form a network that promotes physical gelation of the matrix medium. Previous studies have investigated the mechanism of DBS-induced gelation and the features of DBS-containing gels in poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). In this work, we examine the effect of adding DBS to a series of amphiphilic PPG-b-PEG-b-PPG triblock copolymers differing in composition and molecular weight. Dynamic rheological measurements reveal that the resultant gels are thermoreversible (i.e., they exhibit comparable mechanical properties before dissolution and after reformation under quiescent conditions), exhibiting a maximum in the elastic modulus (G') at temperatures near the gel dissolution (T(d)) and formation (T(f)) temperatures. Both T(d) and T(f) tend to increase with increasing DBS concentration and PPG content, and their difference decreases with increasing PPG fraction in the copolymer. The magnitude of G' is sensitive to copolymer composition and polymer identity at low DBS concentrations, but becomes polymer-independent as the DBS network saturates at concentrations in excess of approximately 1 wt%.
1,3:2,4-二亚苄基-D-山梨醇（DBS）分子能够通过氢键和π相互作用等分子间力自组装成纳米级纤维。在足够高的浓度下（通常小于约2 wt%），纳米纤维可以形成促进基质介质物理凝胶化的网络。先前的研究已经探究了DBS诱导凝胶化的机制以及聚乙二醇（PEG）和聚丙二醇（PPG）中含DBS凝胶的特性。在这项工作中，我们研究了向一系列组成和分子量不同的两亲性PPG-b-PEG-b-PPG三嵌段共聚物中添加DBS的效果。动态流变学测量表明，所得凝胶是热可逆的（即，在静态条件下，它们在溶解前和重新形成后表现出相当的机械性能），在接近凝胶溶解温度（T(d)）和形成温度（T(f)）时弹性模量（G'）出现最大值。T(d)和T(f)都倾向于随着DBS浓度和PPG含量的增加而升高，并且它们的差值随着共聚物中PPG比例的增加而减小。在低DBS浓度下，G'的大小对共聚物组成和聚合物种类敏感，但当DBS网络在超过约1 wt%的浓度下饱和时，G'变得与聚合物无关。
