Protocol for Studying Aqueous Foams Stabilized by Surfactant Mixtures

Abstract

Even though foams have been the subject of intensive investigations over the last decades, many important questions related to their properties remain open. This concerns in particular foams which are stabilized by mixtures of surfactants. The present study deals with the fundamental question: which are the important parameters one needs to consider if one wants to characterize foams properly? We give an answer to this question by providing a measuring protocol which we apply to well‐known surfactant systems. The surfactants of choice are the two non‐ionic surfactants n‐dodecyl‐β‐d‐maltoside (β‐C12G2) and hexaethyleneglycol monododecyl ether (C12E6) as well as their 1:1 mixture. Following the suggested protocol, we generated data which allow discussion of the influence of the surfactant structure and of the composition on the time evolution of the foam volume, the liquid fraction, the bubble size and the bubble size distribution. This paper shows that different foam properties can be assigned to different surfactant structures, which is the crucial point if one wants to tailor‐make surfactants for specific applications.

On the Influence of Intersurfactant H-Bonds on Foam Stability: A Study with Technical Grade Surfactants

“…2) the distribution is much narrower for Plantacare 1200UP. Thus, the surfactant layer can pack more densely and the surface roughness is lower [10] as compared to surfactant layers containing a broader range of chain lengths with chains as short as C 8 . The denser packing and lower surface roughness is known to increase the surface elasticity [10] and thus the foam stability [8,11,12].…”

“…The FoamScan uses conductivity measurements and image analysis to monitor the foam volume V foam and the liquid fraction of the foam e.Ad- ditionally, the bubble sizes and bubble size distributions can be analyzed with the cell size analysis (CSA) function. A detailed description of the FoamScan method can be found in [8,9]. Briefly, the FoamScan device consists of a round glass column (Ø 35 mm) with one flat side which has (a) five pairs of electrodes to measure the foam conductance and (b) four glass prisms on the flat side where pictures of the foam can be taken using one of the two CCD cameras.…”

“…All measurements were performed at room temperature (22 8C) and were carried at least two times for each surfactant. In order to determine the bubble size distribution and the respective arithmetic average bubble radius <r>, all foam pictures were treated with ImageJ and analysed with the new Cell Size Analysis (CSA) software as described in [8]. We characterized the bubble size distributions with the polydispersity index PI (or normalized standard deviation).…”

“…Det. 55 (2018) 1 Figure 5 Original FoamScan images (right) of the foam bubbles stabilized by Plantacare 1200UP and respective bubble size distributions n/n total (left) plotted versus the bubble radius r calculated from the images which were treated using ImageJ program as explained in [8] Tenside Surfactants Detergents downloaded from www.hanser-elibrary.com by 34.216.127.252 on May 12, 2018 For personal use only. studied aqueous surfactant solutions have the same foamability and the generated foams are stable during foam formation.…”

“…55 (2018) 1 For personal use only. Figure 8 Original FoamScan images (right) of foam bubbles stabilized by Texapon N70LS and respective bubble size distributions n/n total (left) plotted versus the bubble radius r calculated from the images which were treated using ImageJ program as explained in [8] Tenside Surfactants Detergents downloaded from www.hanser-elibrary.com by 34.216.127.252 on May 12, 2018 and water) to hydrophilic (water). Thus Texapon N70LS follows this pattern, which, in turn, explains the high surfaceactivity of this surfactant (surprisingly low cmc for a C 12 chain!).…”