A method for benzene/acetonitrile separation using extractive distillation is presented, and dimethyl sulfoxide (DMSO) is selected as the entrainer. Steady state and dynamic simulations for this process are implemented by commercial simulators (Aspen Plus and Aspen Dynamics). On the basis of global economic optimization, a design with optimized operation conditions for this process is developed. Two single temperature control structures with fixed reflux ratio or fixed reflux-to-feed ratio and a dual-end temperature control structure for entrainer recovery column are presented to evaluate the dynamic performance with feed flow rate and feed composition disturbances, and the last structure is quite effective.

Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM). The various critical concentrations and the enthalpy changes of the corresponding phase transitions for the oppositely charged system were obtained from the plots of the observed enthalpy change (ΔHobs) and turbidity measurements as a function of gemini concentration. The morphologies of the aggregates in various phases were observed by Cryo-TEM. Altogether these results suggest the critical role of gemini as a dual linker. At the concentrations where the crosslink between the pendant aggregates happens, the free gemini concentration is proximately zero and the aggregate retains its negative charge. The analysis of various factors involved in the interaction allowed a rationalization of the driving forces for mixed aggregate formation, which will contribute to a subsequent rational design of drug delivery systems based on this polymer/surfactant system.

Four new Y-shaped miktoarm amphiphilic copolymers were synthesized by ring-opening polymerization (ROP) and click chemistry. The structure of these copolymers was determined by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). The stereocomplexes were prepared by an evaporation method and confirmed by FT-IR, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Further the aggregation behaviors of these synthesized polymers and their stereocomplexes were studied by fluorescence spectroscopy (PL), transmission electron microscopy (TEM) and light scattering (LS). Their critical micelle concentrations (CMC) obtained by PL were 0.005 mg mL−1 for MPEG1.9k–(scPLA4.5k)2 and 0.039 mg mL−1 for MPEG5k–(scPLA4.5k)2. The aggregation morphologies of homochiral copolymers were worm-like aggregates, while for the stereocomplexes, the spherical micelles were visually observed. The biocompatibility of these copolymers and their stereocomplexes was evaluated with relatively lower cytotoxicity. Finally, the release of doxorubicin (DOX) encapsulated into the micelles in buffer at pH 5.4 was faster than that at pH 7.4. This study demonstrates that the DOX-loaded stereocomplex micelles could be a potential carrier for cancer treatments.

Novel dumbbell-shaped amphiphilic copolymers ((PLLA)2–G1–P188–G1–(PLLA)2 and (PDLA)2–G1–P188–G1–(PDLA)2) and linear-shaped amphiphilic copolymers (PLLA–P188–PLLA and PDLA–P188–PDLA) were synthesized by click chemistry and ring opening polymerization (ROP). The stereocomplexes (scPLA)2–G1–P188–G1–(scPLA)2 and scPLA–P188–scPLA were prepared and confirmed by X-ray diffraction (XRD). The stereocomplex interaction between PLLA and PDLA was firstly analyzed using microscale thermophoresis (MST) technology and the dissociation constant (Kd) was obtained as 342 μM. The aggregation behaviors of these stereocomplexes were studied using fluorescence spectroscopy, transmission electron microscopy (TEM) and light scattering (LS). The critical aggregate concentration (CAC) obtained from fluorescence measurements was 0.021 mg mL−1 for (scPLA)2–G1–P188–G1–(scPLA)2 and 0.042 mg mL−1 for scPLA–P188–scPLA. These stereocomplexes can self-associate in aqueous solution into spherical aggregates with a diameter of 181 nm for (scPLA)2–G1–P188–G1–(scPLA)2 and 222 nm for scPLA–P188–scPLA. Furthermore, the biocompatibility of the stereocomplexes was evaluated with a relatively lower cytotoxicity. Finally, DOX was encapsulated into the stereocomplex aggregates to evaluate the drug release ability in phosphate buffer at a pH value of 7.4 or 5.4. The drug loading content and the encapsulation efficiency of the aggregates are 9.8%, 54% for (scPLA)2–G1–P188–G1–(scPLA)2 and 8.2%, 45% for scPLA–P188–scPLA. The release of DOX at pH 5.4 is faster than that at pH 7.4. The pH value has a greater effect on the release rate of DOX from dumbbell-shaped stereocomplex aggregates than that from the linear-shaped ones, which ensures the long blood circulation and the higher DOX-release surrounding the tumor site.

•ITC provided thermodynamic characterization of self-association of oppositely charged gemini/SDS surfactants.•Phase transitions and corresponding enthalpies were obtained by ITC.•The transitions reflect a change in morphology, supported by Cryo-TEM images.•Conductivity and ITC results show very good agreement.•An asymmetric distribution of surfactants in the aggregates is supported by results.The thermodynamics and phase behavior of mixtures of cationic gemini surfactant decanediyl-α,ω-bis(dodecyldimethylammonium bromide) (12-10-12) and sodium dodecylsulfate (SDS) were studied in the dilute SDS-rich region. The enthalpy of interaction between both surfactant monomers before the critical micelle concentration for the mixture (cmcmix) was determined by isothermal titration calorimetry (ITC). After the cmcmix, ITC results exhibited a first process associated with a large endothermic enthalpy change followed by a second one with a very small exothermic enthalpy change. In the same regions, the conductivity curves show an increase in slope after the break, followed by a plateau region, respectively for the two processes. The combined results from the various methodologies used lead us to propose that the first process reflects the formation of non-spherical micelles and the second one the vesicle formation. The area per catanionic complex was obtained through surface pressure measurements, leading to an apparent packing parameter ⩾1. The observed behavior may be rationalized on the basis of the hypothesis that both surfactants distribute asymmetrically in the vesicle bilayers and unevenly in the non-spherical micelle. In order to get structural information Cryo-TEM experiments were performed, which provided images that support this interpretation. From all the information gathered a phase diagram was mapped, including three one-phase regions of spherical micelles, non-spherical micelles and vesicles.

Two new amphiphilic linear-dendritic block copolymers (LDBCs) composed of poly(ethylene oxide) (PEO) and a dendron derived from 2,2′-bis(hydroxymethyl)propionic acid (bis-MPA), PEO(5k)-b-G3-(C18H35O2)8 and PEO(5k)-b-G3-(C2H3O2)8 were synthesized by click chemistry. The structures of the LDBCs were determined by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). Furthermore, their aggregation behaviors at 298.15 K for these two synthesized polymers were studied by fluorescence spectroscopy and isothermal titration calorimetry (ITC). The fluorescence measurements indicate that both of the synthesized polymers have evident aggregation behavior in aqueous solution due to the significant hydrophobic interactions between the branched groups. Thus we characterized the thermodynamics of their aggregation by ITC and obtained their critical micelle concentrations (CMC), as well as the positive enthalpy of micellization for (PEO(5k)-b-G3-(C18H35O2)8), which suggests that its molecular self-assembly process is entropy-driven. Furthermore, the micellar morphologies of the copolymers in aqueous solution were verified by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The spherical polymeric micelles of PEO(5k)-b-G3-(C18H35O2)8 and PEO(5k)-b-G3-(C2H3O2)8 were observed and their diameters are 70 nm and 160 nm, respectively. The length of the alkyl chain of the periphery carboxylic acid affects their CMCs and the size of micelles. Finally, the biocompatibility of both LDBCs was evaluated, and they were found to have relatively low cytotoxicity, which provides potential opportunities for a variety of biomedical applications.

•ITC and conductivity provide critical concentrations for these complex systems.•OD helps the understanding of their structural changes.•ITC provides the enthalpies accompanying the various processes in the mixed systems.•The cmcmix are smaller than cmc for pure surfactants indicating a synergistic effect.•The gemini spacer length influences its aggregation behavior with NaCA.The thermodynamics of the process of self-assembly of cationic gemini surfactants, [C12H25(CH3)2N(CH2)SN(CH3)2C12H25]Br2, (the spacer S being 2, 6 or 10, assigned as C12CSC12Br2) and the system of oppositely charged mixture of surfactants formed by C12CSC12Br2 and sodium cholate (NaCA) in aqueous solution has been investigated by isothermal titration calorimetry (ITC), conductivity and turbidity measurements. The critical micelle concentration values (cmc) for the gemini surfactants C12CSC12Br2 obtained from calorimetry and conductivity were found to be consistent with values reported in the literature. The enthalpies of micellization (ΔHmic) of C12CSC12Br2 are all exothermic, presenting a strong negative minimum at S = 6, corresponding to the maximum in the cmc values. For the mixed system of oppositely charged surfactants (C12CSC12Br2(S = 2, 6, 10)/NaCA), we did obtain from ITC the critical parameters for different events that take place as the concentration of gemini surfactant increases, such as the formation of NaCA-rich mixed micelles (cmcmix, ΔHmic-mix), the formation of a precipitate (immiscible liquid crystalline (LC) phase) (CP, ΔHP) and its re-dissolution (CR, ΔHR), and finally the formation of positive charge-rich mixed micelles (CM, ΔHM). It should be stressed that the values of cmcmix (gemini) are much smaller than those for pure gemini and pure NaCA. These results also show that there is a stronger synergistic effect between the two surfactants in the NaCA-rich region. The turbidity measurements proved valuable to the determination of the region of immiscible LC phase. The ITC results are combined with those obtained by conductivity and turbidity leading to a thorough discussion of the effect of the gemini spacer length on the aggregation behavior of the mixed systems.Graphical abstract

Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM). The various critical concentrations and the enthalpy changes of the corresponding phase transitions for the oppositely charged system were obtained from the plots of the observed enthalpy change (ΔHobs) and turbidity measurements as a function of gemini concentration. The morphologies of the aggregates in various phases were observed by Cryo-TEM. Altogether these results suggest the critical role of gemini as a dual linker. At the concentrations where the crosslink between the pendant aggregates happens, the free gemini concentration is proximately zero and the aggregate retains its negative charge. The analysis of various factors involved in the interaction allowed a rationalization of the driving forces for mixed aggregate formation, which will contribute to a subsequent rational design of drug delivery systems based on this polymer/surfactant system.