Thomas O’Lenick – SurfaTech Corporation, US …

1 Tony O'Lenick PhD Siltech LLC, US SILICONES. Thomas O'Lenick SurfaTech corporation , US.. PEG/PPG dimethicone structure and function PEG/PPG dimethicone compounds should ABSTRACT. be used in instances where they provide benefits that cannot be obtained by organic Despite the increasing usage of silicone polymers in personal care products, the compounds. These properties include: selection of the proper polymer for a particular application remains somewhat elusive. w Lowering of surface tension (into the This directly results in inefficiency of formula development.)

2 This problem is exacerbated range of 25 dynes/cm). by the reliance upon INCI names in selection of compounds. While helpful in placing w Provide unique skin feel. polymers in a generic class, it is of limited help in optimising formulation efficiency. w Provide unique emulsification properties Compounds that are water insoluble, water dispersible or water insoluble can all share (especially in invert emulsions). a common INCI name. Likewise polymers that provide wetting, emulsification, or w Provide film formation. conditioning can share a common INCI name.

3 This article is intended to clarify w Provide foaming of non-traditional selection of products for formulation. formulations. These properties are a direct result of the structure, but the structure needs to be In studio for carefully selected. PEG/PPG dimethicone new artwork polymers have increased polarity, by virtue of their polyoxyalkylene groups. It is important to note that these modifications are done by chemical reaction between a reactive silicone and a vinyl containing compound. A very common structure is shown in Figure 1.

4 Figure 1: PEG/PPG dimethicone structure. There are several variables that can be modified to change the performance of the Surface tension DMC polymer. One of the most important When added into water at low is the ratio of a (silicone soluble portion) concentrations, PEG/PPG dimethicone to b (water soluble portion) as well as the (DMC) migrates to the air/water interface. total number of a and b, both of which are As more DMC is added into the water, the important to functionality. The higher the interface becomes saturated and a critical ratio of a to b the less water soluble the point is achieved.

5 When additional DMC. In studio for product. Also, the molecular weight of polymer is added, it cannot migrate to the new artwork the DMC polymer can drastically change interface, so they start to form micelles. properties. The studies presented in this This critical point where the interface is paper keep the ratio of D/D* constant (that saturated and micelles start to form is is the ratio of a/b is kept constant relative called the critical micelle concentration to each other). (CMC). Critical micelle concentrations are Figure 2: Illustration of Table 1: Surface tension and molecular weight.

6 PEG 8 dimethicone ( solution). PEG 8 dimethicone ( wt% solution). Product Molecular Surface weight tension (dynes/cm). In studio for A 607 new artwork B 808 C 1108 D 1610 E 2111 Figure 3: Graphic surface tension and molecular weight. April 2013 P E R S O N A L C A R E 1. SILICONES. In studio for In studio for new artwork new artwork Figure 4: Contact Figure 5: Wetting time (seconds) versus molecular weight. determined by monitoring surface tension. formulation. As will become clear Table 2: Function of dimethicone Figure 2 shows an illustration of what subsequently, interaction with other raw copolyol versus molecular weight.

7 Happens upon addition of a surfactant materials in the formulation needs to be into bulk solution. considered as well. Molecular weight (Da) Function The surface tension starts to decrease The surface tensions are related to 500 Wetting in a linear relationship with the amount the molecular weight of a series of PEG 8. of surfactant added. The moment the dimethicone in which the ratio of silicone 2500 Emulsification interface gets saturated, the surface units to polyoxyalkylene units (a:b) are 10000 Conditioning tension stops decreasing.

8 Kept constant but increases. The results 50000 Waterproofing The key to surface tension efficiency is are shown in Table 1 and Figure 3. the ability of a polymer to migrate to the The structure/function relationship is Table 3: Draves wetting. interface and take up the maximum free seen in these same compounds in both volume on that interface. This maximisation wetting times and eye irritation as shown Sample Wetting time of free volume at the interface and its below. (Seconds). affinity for the interface makes the DMC.

9 A 607 extremely effective at lowering surface Wetting properties as a tension. This leads to DMC being used function of molecular weight B 808 at very low concentrations to drastically The term wetting' refers to how a material C 1108 change the properties of a solution. coats a surface. For example, if a water D 1610 The molecular weight is a key concept in drop is placed onto a lotus leaf, the water E 2111 determining CMC. As the molecular weight will minimise the interaction with the leaf increases, the CMC decreases.

10 This is due and have a high contact angle. If a good in part to the fact that the surface can wetting agent is added either to the surface Table 4: PEG 8 dimethicone 1% foam test. accommodate fewer large molecules' of the leaf or in the water solution that Sample Immediate 3 minutes than small molecules. The CMC of a DMC same drop will spread out coating the is a key property to be determined before surface of the leaf, in turn making the leaf A 607 90 62. using a specific DMC in formulation, this wet', and this is where the term wetting B 808 90 63.