## 3 Results
### Composite Membrane Characterisation: Before and after Exposure to ABE-Fermentation Broth
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Membrane** & **Condition** & **\(\mathbf{\Theta}\) by Water** & **\(\mathbf{\Theta}\) by Acetone** & **\(\mathbf{\Theta}\) by Ethanol** & **\(\mathbf{\Theta}\) by Butanol** \\ \hline MDK-3 & initial & \(88\pm 2\) & \(41\pm 2\) & \(23\pm 2\) & \(26\pm 2\) \\ after ABE & \(74\pm 1.8\) & \(32\pm 1\) & \(21\pm 2\) & \(20\pm 1.3\) \\ \hline PHeptMS & initial & \(103\pm 2\) & \(31\pm 2\) & \(37\pm 2\) & \(23\pm 2\) \\ after ABE & \(91\pm 2\) & \(25\pm 1.6\) & \(34\pm 1.4\) & \(21\pm 1.1\) \\ \hline PDecMS & initial & \(106\pm 2\) & \(36\pm 2\) & \(41\pm 2\) & \(28\pm 2\) \\ after ABE & \(88\pm 1.3\) & \(24\pm 2.1\) & \(35\pm 1.2\) & \(23\pm 1.7\) \\ \hline \end{tabular}
\end{table} 
Table 3: Contact wetting angles of the membranes before and after exposure to the ABE-fermentation broth (\(\theta\), \({}^{\circ}\)). in the length of the side radical from C\({}_{7}\) to C\({}_{10}\), the value of the contact angle tends to increase. This indicates an increase in their hydrophobicity as well as the remote interaction parameter. The MDK-3 Carbosil(r) commercial membrane in the studied membrane series has the lowest hydrophobicity (88\({}^{\circ}\)); thus, one should expect the highest water flux through it and the lowest alcohol/water selectivity among the membranes under study. The membranes studied have a high degree of wetting of the target components (\(\theta<90^{\circ}\)). It is worth noting that the lowest contact angles with acetone, ethanol, and butanol were shown by the PHeptMS membrane. The low contact angles of the PHeptMS membrane predict high separation factors in the ABE-fermentation broth pervaporation process. Moreover, the obtained data correlate well with the data of [43], which demonstrated high selectivity of separation of butanol from the mixture (94) with water. The PHeptMS membrane material in comparison with PDMS and polycylmethylsiloxane (POMS) demonstrated the highest selectivity of separation of C\({}_{2}\)-C\({}_{4}\) alcohols from water. After exposure of the selective layer of the membranes in the fermentation broth, a change in the contact wetting angle with respect to the studied substances (water, butanol, acetone, and ethanol) was observed. The general trend was a decrease in the contact wetting angle for all solvents. The largest relative drop in the angle was recorded for water: by 15, 12, and 17% for MDK-3, PHeptMS, and PDecMS, respectively. The observed phenomenon correlates with the presence of a peptide film on the surface of the membrane selective layer after contact with the broth, as shown by SEM, EDX, and IR data. Such a film appears to reduce the hydrophobicity of the surface of polysiloxane membranes and increase their affinity to the ABE mixture. Thus, the water contact angle for the MDK-3 membrane decreased by about 1.2 times compared to the value for the original membrane. For the PDecMS membrane, a stronger decrease in hydrophobicity was observed--the water contact angle decreased by 17% compared to the pure surface of the selective layer. More stable values of the contact angle of wetting after contact with the fermentation medium were characteristic of the PHeptMS membrane. This was characterized by a decrease in the value of the contact angle of wetting with water by about 12% compared to the original membrane. Comparison of the Peraporation Properties of Composite Membranes before and after Exposure to ABE-Fermentation Broth  
To assess the effect of membrane clogging on its transport properties, the PHeptMS, PDecMS, and MDK-3 composite membranes were studied in the process of pervaporation separation of real fermentation broth before and after continuous contact with it for one month. The difference between the ABE-fermentation broth and the model solution lies not only in the different density, pH, and viscosity, but also in the presence or absence of inorganic salts, glucose, active and inactive microbial cells, and some other metabolic compounds.