Nanoparticle and gelation stabilized functional composites of an ionic salt in a hydrophobic polymer matrix

Abstract

Polymer composites consisted of small hydrophilic pockets homogeneously dispersed in a hydrophobic polymer matrix are important in many applications where controlled release of the functional agent from the hydrophilic phase is needed. As an example, a release of biomolecules or drugs from therapeutic formulations or release of salt in anti-icing application can be mentioned. Here, we report a method for preparation of such a composite material consisted of small KCOOH salt pockets distributed in the styrene-butadiene-styrene (SBS) polymer matrix and demonstrate its effectiveness in anti-icing coatings. The mixtures of the aqueous KCOOH and SBS-cyclohexane solutions were firstly stabilized by adding silica nanoparticles to the emulsions and, even more, by gelation of the aqueous phase by agarose. The emulsions were observed in optical microscope to check its stability in time and characterized by rheological measurements. The dry composite materials were obtained via casting the emulsions onto the glass substrates and evaporations of the organic solvent. Composite polymer films were characterized by water contact angle (WCA) measurements. The release of KCOOH salt into water and the freezing delay experiments of water droplets on dry composite films demonstrated their anti-icing properties. It has been concluded that hydrophobic and thermoplastic SBS polymer allows incorporation of the hydrophilic pockets/phases through our technique that opens the possibility for controlled delivering of anti-icing agents from the composite.

Figure 1. Schematic representation of the steps for casting of solutions prepared with aqueous KCOOH solution suspended in SBS polymer (a) without particle stabilization, or (b) with particle stabilization.

Figure 2. Optical microscope images of wet emulsions with internal volume fraction φ = 25% (v/v) prepared by different stabilization methods for immediately after and 3 minutes after preparation of emulsions.

(a) Wet emulsions without stabilizing agent, (b) wet emulsions prepared with SDS surfactant as the stabilizing agent, (c) wet emulsions prepared by nanoparticle stabilization. Scale bar is 500 µm.

Figure 3. Optical microscope images of emulsions for altered concentrations of nanoparticles and internal phase volume fractions.

Internal phase does not contain agarose gel. (a) Wet and, (b) dry emulsions. Scale bar represents 200 µm.

Figure 4. Optical microscope images of wet and dry emulsions prepared with internal volume fraction Φ = 0.33, and nanoparticle concentration of 0.7% (w/w).

(a) Wet emulsions prepared without agar gel in the dispersed phase, (b) wet emulsions prepared with agar gel in the dispersed phase, (c) dry emulsions prepared without agar gel in the dispersed phase, (d) dry emulsions prepared with agar gel in the dispersed phase. Scale bar is 200 µm.

Figure 5. Optical microscope images of emulsions for altered concentrations of nanoparticles and internal phase volume fractions.

Internal phase contains agarose gel. (a)Wet and, (b) dry emulsions. Scale bar represents 200 µm.

Figure 6. Viscosity versus shear rate profiles for emulsions with (a) no gelation of the internal phase, (b) gelation of the internal phase.

Viscosity versus shear rate profile for homogeneous SBS solution has been included for comparison. Data indicates the average of at least three observations with corresponding standard deviations.

Figure 7. Water contact angle (WCA) measurements on functional membranes with gelation of internal phase.

Each series represents an internal volume fraction as displayed in the legend. Horizontal axis represents particle concentration in % (w/w). (a) Immediately after deposition of water droplets on the surface, (b) 15 seconds after water droplet deposition on the surface. On membranes with 0.7% (w/v) nanoparticle stabilization, the water contact angle decreased to 0 for 14% (v/v) and 25% (v/v) internal volume fractions. Data indicates the average of at least three observations with corresponding standard deviations.

Figure 8. Effect of internal phase volume fraction and nanoparticle concentration on profile of potassium formate release from dry composite membranes with gelation of the internal phase.

Data indicates the average of at least three observations with corresponding standard deviations.

Figure 9. Average freezing times water droplets on dry composite membranes with gelation of the internal phase, SBS (control) and SBS with 1.0% nanoparticle concentration (control).

The inset image is taken from temperature and humidity controlled chamber, where the composite with 1% (w/v) nanoparticle concentration (left, Φ = 0.25) and 0.7% (w/v) nanoparticle concentration (right, Φ = 0.25) was monitored at 60 minutes (plate temperature: −14°C, ambient temperature: 5°C). Data indicates the average of at least three observations with corresponding standard deviations.