"Tying up loose ends" – silicone surfactants as stabilizing agents for flexible polyurethane foam

Abstract

This paper is a tribute to the work of Dr. Michael J. Owen and colleagues in revealing the mechanism of the silicone surfactant-driven stabilization of flexible polyurethane foam. This work, performed at Midland Silicones (acquired by Dow Corning Corporation in 1967), was the inspiration for a body of experimental and theoretical research performed by the present authors in the mid-1990's. For flexible polyurethane foam, the surfactant is necessary to stabilize the liquid foamy mass before it hardens into an elastomeric sponge. Owen and coworkers demonstrated that in order to stabilize the foam the surfactant must (1) significantly lower the equilibrium surface tension of the liquid, (2) exhibit a dynamic surface tension within a narrow range of values, and (3) have an appreciable but low surface viscosity. The recent work of the authors has both validated these observations and extended their scope. They have modeled the stabilization process and have found that stability is the result of a delicate interplay of surface viscosity and elasticity which are functions of both structure and excess surface concentration of the surfactant. This modeling work was validated experimentally by investigating the drainage of model polyurethane thin liquid films ("soap films") containing silicone surfactants. The seminal nature of the work done by Owen and coworkers was reinforced by the authors' discovery that many of the original conclusions were validated by the recent work.

Polysiloxane‐Based Block Copolymers as Structure‐Directing Agents in the Synthesis of Hierarchically Organized Silica Monoliths

“…Its slope for the adsorption branch is less steep than for the other silica gels. The results of the corresponding SAXS measurements confirm this trend with a less pronounced diffraction peak for d 1 . SEM images (Figure 7) of the corresponding silica gels show a reduction of the interconnectivity of the macropores with increasing HCl concentration.…”

“…Silicone surfactants have become a commercially important class of surfactants with a wide range of applications from the synthesis of polyurethane foams, [1,2] as additives for coatings and paints to softening agents in cosmetic products, etc. [3][4][5][6][7][8][9][10][11] Especially amphiphilic siloxane surfactants containing a hydrophilic block, typically a polyethylene oxide (PEO) block, and a hydrophobic block of e.g., polydimethylsiloxane (PDMS), have attracted attention as these surfactants show a strong surface activity in polar solvents, such as aqueous solutions.…”

Synthesis and evaluation of some derivatives of polysiloxanes

“…One result of the low interfacial tension of silicone surfactants is their vigorous adsorption at the organic/air interface [10][11][12][13][14].…”

Conservation laws of surfactant transport equations

“…where γ (s) denotes the surface density of the physical quantity investigated, u is the material velocity, H (s) = ∇ s · n (s) is the total surface curvature, n (s) is the unit normal vector of the interface S, pointing from the domain B (1) into the domain B (2) , (1) denotes the jump of the quantity G over the interface S between the phases B (1) and B (2) , φ (i) (i = 1, 2) and φ (s) are the respective non-convective fluxes in the bulk phases (i = 1, 2) and on the interface S, π (s) is the surface production/supply rate density, and ∇ (s) indicates the surface gradient operator, respectively. For the case of a material interface, assuming that the interfacial non-convective flux φ (s) is tangential to the interface, an equivalent formulation of (1) is provided in Ref.…”

“…To outline a few examples, silicone surfactants are used as stabilizing agents for polyetherane foam by reducing interfacial tension and, consequently, promoting the formation of a coherent interfacial film. 1 Also, surfactants are used to control the formation of small droplets in industrial emulsification processes by lowering the surface tension, and hence facilitating the droplet breakup and preventing coalescence. 2,3 The delivery of surfactants into the lung helps to regulate its surface tension with prematurely born infants with a lung surfactant deficiency.…”