Polyelectrolytes in alcohol-water mixtures: From counterion solvation to hand sanitisers

洗手液是防止传染病传播的重要工具。与用肥皂洗手不同，它们可以很容易地使用，而不需要自来水源。洗手液通常由80 v/v酒精和20 v/v水组成，pH值为中性。最常用的酒精是乙醇和异丙醇。水-醇混合物是低粘度液体，这一特征限制了它们的功效。为了克服这个问题，可以加入聚合物，然而，洗手液的高醇含量意味着普通聚合物不能用作增稠剂，因为它们在醇介质中的溶解度差。我们提出了一个简单的方法，以提高聚电解质在醇-水混合物中的溶解度，通过使用疏水抗衡离子。聚电解质已经广泛用作水基制剂中的药物和食品中的胶凝剂。初步实验表明，虽然羧甲基纤维素的钠盐不溶于几乎所有的非水溶剂，但其四丁基铵盐容易溶于醇和醇-水混合物以及其它有机介质。 离子交换方法原则上可用于任何离子（生物）聚合物，并且具有不需要合成新聚合物的优点。 适用于大量的聚合物，包括一些非常广泛生产的生物聚合物，在需求突然激增的情况下的供应问题可以用所提出的方法来解决。羧甲基纤维素或藻酸盐已经被联邦药品管理局和欧洲药品管理局批准，许多季铵盐也是如此。从基本的角度来看，具有疏水离子的聚电解质在醇（和其他有机介质）中的溶液是有趣的，因为它们的热力学性质是由充满活力的反离子-溶剂相互作用决定的，而不是反离子熵，这是迄今为止研究的大多数系统所共有的。最近的发展，在模拟技术，特别是由道格拉斯和同事，强调了反溶剂化的重要作用。因此，在过去的五年里，反溶剂化引起了人们的广泛关注，它被认为是理解经典理论无法解释的聚电解质的一些关键构象、散射和流变性质的关键因素。关键的挑战是理解反熵、反溶剂化和聚合物-溶剂相互作用对相行为的影响，聚电解质在混合醇-水溶液中的结构和流变性。虽然这项工作的动机是聚电解质在洗手液中的潜在应用，但这项建议中产生的知识将导致我们对热力学的基本理解大幅增加。

Hand sanitisers are an important tool to combat the spread of infectious diseases. Unlike hand-washing with soap, they can be readily used without the need of a running water source. Hand sanitisers are typically composed of 80 v/v alcohol and 20 v/v of water at neutral pH. The most common alcohols used are ethanol and isopropanol. Water-alcohol mixtures are low viscosity liquids, a feature that limits their efficacy. To overcome this problem, polymers could be added, however, the high alcohol content of hand sanitisers means that common polymers cannot be used as thickening agents due to their poor solubility in alcohol media. We propose a simple method to improve the solubility of polyelectrolytes in alcohol-water mixtures by using hydrophobic counterions. Polyelectrolytes are already in wide use as gelling agents in pharmaceutical and food products in water-based formulations. Preliminary experiments show that while the sodium salt of carboxymethyl cellulose is insoluble in practically all non-aqueous solvents, its tetrabutyl-ammonium salt readily dissolves in alcohols and alcohol-water mixtures and other organic media. The ion-exchange approach can in principle be used for any ionic (bio-)polymer and has the advantage that it does not require the synthesis of new polymers. Being applicable to a large number of polymers, including some very widely produced biopolymers, the issue of supply in case of a sudden spike in demand can be tackled with the approach proposed. Carboxymethyl cellulose or alginate are already approved by the Federal Drug Agency and European Medicine Agency as are many quaternary ammonium salts. From the fundamental perspective, solutions of polyelectrolytes with hydrophobic ions in alcohols (and other organic media) are interesting because their thermodynamic properties are dictated by energetic counterion-solvent interactions, instead of counterion entropy, as is common for most systems studied thus far. Recent developments in simulation techniques, particularly by Douglas and co-workers, have highlighted the important role of counterion solvation. Counterion solvation has therefore attracted much attention in the last five years and it is thought to be a crucial factor in understanding some of the key conformational, scattering and rheological properties of polyelectrolytes which classical theories are unable to explain.The key challenges are to understand the influence of counterion entropy, counterion solvation, and polymer-solvent interactions on the phase behaviour, structure and rheology of polyelectrolytes in mixed alcohol-water solutions. While the work is motivated by the potential application of polyelectrolytes in hand sanitisers, the knowledge generated in this proposal will lead to a substantial increase in our fundamental understanding of polyelectrolyte thermodynamics.