A Brief Review of Polymer/Surfactant Interaction

Feb 1, 2004 | Contact Author | By: Robert Y. Lochhead and Lisa R. Huisinga, The Institute for Formulation Science, The University of Southern Mississippi
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Title: A Brief Review of Polymer/Surfactant Interaction
polymerx surfactantx polymer-surfactant interactionx conditioning shampoosx
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Keywords: polymer | surfactant | polymer-surfactant interaction | conditioning shampoos

Abstract: In this article, the significance of parameters such as correlation length (blob size), micelle structure, comicellization, polymer adsorption conformation and coacervate structure are introduced with relevance to the conceptual appreciation of polymer-surfactant interactions and its bearing on recent advances in conditioning shampoos.

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RY Lochhead and LR Huisinga, A Brief Review of Polymer/Surfactant Interaction, Cosm & Toil 119(2) 37-46 (Feb 2004)

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This brief review of polymer-surfactant interaction opens by describing how polymers behave in solution. Then we survey the literature on the interaction of nonionic polymers with surfactants, and the interaction of polyelectrolytes with ionic surfactants of opposite charge. After a brief discussion of polymer adsorption at interfaces, we consider the implications of these interactions on the design of shampoo products.

Polymers in Dilute and Semi-dilute Solution

Polymer-surfactant interaction in personal care compositions usually occurs in aqueous media. In order to understand the concepts of this type of polymer-surfactant interaction, it is first necessary to grasp how typical polymers behave in solution. The condition for a polymer molecule to dissolve is that the polymer-solvent interaction is greater than both polymer-polymer and solvent-solvent interactions. If this condition is achieved the polymer will dissolve and, depending upon the concentration, a dilute solution or semi-dilute solution will be formed.

A dissolved polymer can occupy many times the volume of the polymer molecule itself—that is, a polymer swells when it is dissolved and the volume inside the swollen polymer contains solvent. It is not unusual for a dissolved polymer to be swollen to a thousand times its original size. In a dilute solution each dissolved polymer molecule will be isolated. If the polymer concentration is increased, eventually there comes a point when the entire space is filled with swollen polymer molecules and above this concentration the polymer can only occupy the solution if the molecules entangle and thread through each other’s domains.

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Figure 1. Blobs in dilute to semi-dilute solutions

Figure 1. Blobs in dilute to semi-dilute solutions

In dilute solution, the blob size is the size of the entire polymer molecule and in semi-dilute solution the blob size becomes the distance between entanglement points.

Figure 2. The decrease in blob size as the polymer concentration increases

Figure 2. The decrease in blob size as the polymer concentration increases

The blob size decreases as polymer concentration increases even in dilute solution; here, g(r) represents the blob size and the horizontal axis represents polymer concentration.

Figure 3. Polymer-surfactant interaction

Figure 3. Polymer-surfactant interaction

Jones described the T1 point as the lowest surfactant concentration at which interaction occurred between the surfactant and polymer, and T2 as the surfactant concentration at which both the polymer and the air-water interface became “saturated” with surfactant and normal micelles first appeared.

Figure 4. Comicellization of polymer hydrophobes with surfactant hydrophobes (hydrophobically-modified hydroxyethyl cellulose)

Figure 4. Comicellization of polymer hydrophobes with surfactant hydrophobes (hydrophobically-modified hydroxyethyl cellulose)

The addition of surfactant to solutions of this polymer, in the region of the CMC, causes a dramatic increase in viscosity followed by an equally spectacular decrease in viscosity to levels below that measured for the polymer solution in the absence of surfactant.

Figure 5. Effect of surfactant on low shear rheology

Figure 5. Effect of surfactant on low shear rheology

Even small quantities of a low molecular weight surfactant comicellize with the polymer micelles and this results in immediate breakdown of the network structure and loss of the viscosity even at surfactant concentrations well below the CMC.

Figure 6. Interaction of hydrophobically-modified hydrophilic polymer (hydrophobically-modified hydroxyethyl cellulose) with micelles

Figure 6. Interaction of hydrophobically-modified hydrophilic polymer (hydrophobically-modified hydroxyethyl cellulose) with micelles

These large micelles form exceptionally large junction zones, and stoichiometric comicellization with hydrophobically-modified hydrophilic polymers results in a large increase in viscosity that can be maintained over a broad surfactant concentration range.

Figure 7. The schematic illustration of the principle of conditioning shampoos, according to Goddard17, 18

Figure 7. The schematic illustration of the principle of conditioning shampoos, according to Goddard<sup>17, 18</sup>

Goddard showed that polyquaternium-10 and common anionic surfactants formed coacervates that are one-phase systems at shampoo concentrations but they phase separate upon dilution during the shampooing process to deposit conditioning agents on the hair.

Figure 8. Adsorption as mushrooms

Figure 8. Adsorption as mushrooms

This type of interaction has been named “mushroom adsorption” because polymers with one anchor point appear to have a mushroom stem and a “button” made up of the cloud of polymer in its swollen conformation.

Figure 9. Loops, trains and tails

Figure 9. Loops, trains and tails

It is generally accepted that most real polymers possess several anchor groups along the chain and these are adsorbed as trains where the interaction between polymer and surface is high, and as loops and tails where the interaction between the polymer and solvent is high.

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