## 3 Important Factors in Efficacy of Amphiphiles
### Role of Temperature  
Additives such as PEG exhibit only a very small beneficial effect in biomass conversion when used at temperatures lower than 25 \({}^{\circ}\)C [28]. Three hypotheses have been suggested in order to explain this observation. First, the aqueous solubility of PEG was reported to be unlimited for all degrees of polymerization at room temperature [66], which makes the interaction of PEG with hydrophobic sites of biomass (e.g., lignin) weak. According to [PERSON] _et al._[28], PEG (aqueous soluble polymer) demonstrates an inverse solubility, meaning that with an increase of temperature its solubility decreases, and as a result causes this polymer to form a stronger interaction with lignin. It was observed that the adsorption of PEG onto SPS (steam pretreated spruce) was increased by a factor of two as the temperature was increased from 20 \({}^{\circ}\)C to 40 \({}^{\circ}\)C [28]. Studies conducted by [PERSON] _et al._[28] were in agreement with that of [PERSON] _et al._[38], who showed that when the Tween concentration was held at 0.47 g/g glucan (optimum concentration), and the incubation temperature of corn stover with surfactant was increased from 45 \({}^{\circ}\)C to 51 \({}^{\circ}\)C, glucose yields was increased from 59.6% to 65.6%. However, further increasing the temperature to above 51 \({}^{\circ}\)C did not result in an additional positive effect on glucose or xylose yields [38]. [PERSON] _et al._[86] found that the number of water molecules bound per chain of PEG 2000 was \(136\pm 4\) in the free-state and \(210\pm 6\) while attached over micelles. This corresponds to 3.1 to 4.8 water molecules per monomer unit, respectively. The high solubility of PEG in water (determined experimentally) along with its high A\({}_{2}\) [second viral coefficient or excluded volume (v)] and relationship with molecules of water and rapid motion of PEG chains in aqueous medium [being a highly flexible chain with steric factor (\(\sigma\)) of \(\sim\)1] suggest that PEG exists in water as a highly hydrated polymer with a large excluded volume [65,87]. The second hypothesis to explain the effect of temperature on surfactants relates to the fact that PEG conformation is altered by temperature. For example, it was found that PEG experiences contraction and dehydration as temperature rises. This facilitates an enhanced packing density on adsorbed surfaces that enhances the steric repulsion. There are many models or theories that have been developed to describe the parameters that affect the resistance of a polymer-coated surface to non-specific protein adsorption. One of these models, depicted in Figure 2, predicts that each individual polymer chain exist as a mushroom or half sphere (based on the concentration) [88] adsorbed to the surface, that upon compression is squeezed out from the beneath the protein of interest [63]. Studies have shown that these proteins can be desorbed from PEG, based on the conformational changes adopted by this polymer. For instance, the helical or amorphous conformation of PEG was found to be protein resistant whereas the \"all-trans\" conformation was not [89]. Finally, the third hypothesis explaining the increased effectiveness of surfactant-treated systems with increased temperature relates to reduced viscosity. In contrast to the polymer-surfactant system, that retains high viscosity at elevated temperature; solutions containing surfactants or proteins demonstrated a reduced viscosity as the temperature rises [30,90]. According to [PERSON] theory, the viscosity of the solvent is responsible for a friction against protein in solution and results in decreased motion and inhibitory impact on catalysis in motile enzyme [74]. It has been reported that at a low ionic strength (0.003-0.01 M) and neutral or alkaline pH and low temperatures (4 \({}^{\circ}\)C), \(\alpha\) and \(\beta\)-casein occur as monomers.