Cryostructuring of Polymeric Systems. 55. Retrospective View on the More than 40 Years of Studies Performed in the A.N.Nesmeyanov Institute of Organoelement Compounds with Respect of the Cryostructuring Processes in Polymeric Systems

Abstract

The processes of cryostructuring in polymeric systems, the techniques of the preparation of diverse cryogels and cryostructurates, the physico-chemical mechanisms of their formation, and the applied potential of these advanced polymer materials are all of high scientific and practical interest in many countries. This review article describes and discusses the results of more than 40 years of studies in this field performed by the researchers from the A.N.Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences-one of the key centers, where such investigations are carried out. The review includes brief historical information, the description of the main effects and trends characteristic of the cryostructuring processes, the data on the morphological specifics inherent in the polymeric cryogels and cryostructurates, and examples of their implementation for solving certain applied tasks.

Keywords: applied potential; cryogels; cryostructurates; cryostructuring; macroporous morphology; physico-chemical properties.

Figure 1

Micrographs demonstrating the macroporous morphology of various polymeric cryogels. and cryostructurates: (A) PVA-based cryogel (51a in Table 1) formed in a frozen (−20 °C/12 h) aqueous system (10-μm-thick thin section stained with Congo red; transmission optical microscope). (B) Agarose-based cryogel (53a in Table 1) formed in a frozen (−30 °C/1 h followed by −10 °C/23 h) aqueous system (10-μm-thick thin section stained with Cresyl violet; transmission optical microscope). (C) Polystyrene-based cryostructurate formed in the crystallized (+25 °C/4 h) naphthalene followed by its extraction with methanol (1-mm-thick layer; transmission optical microscope). (D) Butadiene-co-styrene-latex-based cryostructurate (65 in Table 1) formed in a frozen (−20 °C/12 h) aqueous system (1-mm-thick layer; transmission optical microscope). (E) Poly(NIPAAM-co-DMAPA)-based cryogel (59 in Table 1) formed in a frozen (−10 °C/20 h) aqueous system (10-μm-thick thin section stained with Bromophenol blue; transmission optical microscope). (F) Poly (acrylamide)-based cryogel (5b in Table 1) formed in a frozen (−8 °C/48 h) formamide using a unidirectional freezing (freeze-dried sample; transmission optical microscope). (G) Bovine-serum-albumin-based cryogel (78b in Table 1) formed in a frozen (−20 °C/18 h) aqueous system (1-mm-thick layer stained with Methylene blue; optical stereomicroscope). (H) Ca-Alginate-based cryostructurate (76 in Table 1) formed in a frozen (−20 °C/1 h) aqueous system followed by freeze-drying and cross-linking with Ca-ions (1-mm-thick layer; transmission optical microscope). (I) Gelatin-based cryogel (59c in Table 2) formed in the medium of frozen DMSO (−20 °C/2 h) followed by its cryoextraction with cold (−20 °C) ethanol (2-mm-thick layer stained with Methylene blue; laser confocal microscope). Not that all these micrographs are from the private archive of the author of the present review and were taken by him personally.

Figure 1

Micrographs demonstrating the macroporous morphology of various polymeric cryogels. and cryostructurates: (A) PVA-based cryogel (51a in Table 1) formed in a frozen (−20 °C/12 h) aqueous system (10-μm-thick thin section stained with Congo red; transmission optical microscope). (B) Agarose-based cryogel (53a in Table 1) formed in a frozen (−30 °C/1 h followed by −10 °C/23 h) aqueous system (10-μm-thick thin section stained with Cresyl violet; transmission optical microscope). (C) Polystyrene-based cryostructurate formed in the crystallized (+25 °C/4 h) naphthalene followed by its extraction with methanol (1-mm-thick layer; transmission optical microscope). (D) Butadiene-co-styrene-latex-based cryostructurate (65 in Table 1) formed in a frozen (−20 °C/12 h) aqueous system (1-mm-thick layer; transmission optical microscope). (E) Poly(NIPAAM-co-DMAPA)-based cryogel (59 in Table 1) formed in a frozen (−10 °C/20 h) aqueous system (10-μm-thick thin section stained with Bromophenol blue; transmission optical microscope). (F) Poly (acrylamide)-based cryogel (5b in Table 1) formed in a frozen (−8 °C/48 h) formamide using a unidirectional freezing (freeze-dried sample; transmission optical microscope). (G) Bovine-serum-albumin-based cryogel (78b in Table 1) formed in a frozen (−20 °C/18 h) aqueous system (1-mm-thick layer stained with Methylene blue; optical stereomicroscope). (H) Ca-Alginate-based cryostructurate (76 in Table 1) formed in a frozen (−20 °C/1 h) aqueous system followed by freeze-drying and cross-linking with Ca-ions (1-mm-thick layer; transmission optical microscope). (I) Gelatin-based cryogel (59c in Table 2) formed in the medium of frozen DMSO (−20 °C/2 h) followed by its cryoextraction with cold (−20 °C) ethanol (2-mm-thick layer stained with Methylene blue; laser confocal microscope). Not that all these micrographs are from the private archive of the author of the present review and were taken by him personally.

Figure 2

Macroporous morphology of the PVA cryogels prepared by the combination of the cryotropic. gel-formation and the additional phase-transformation processes: (A–C) Respectively, the appearance of the stained with Congo red 2-mm-thick disk (68, Table 1) prepared by freezing (−30 °C/0.5 h and then −5 °C/12 h) of the mixed solution containing PVA (7 wt.%) and gum arabic (7 wt.%) and the optical microscopy images of this gel material under different magnifications. (D–F) PVA-based cryogels (72, Table 1) formed by freezing (−11.6 °C/12 h) of the DMSO solutions of the polymer without (D) and with the additives of methanol in concentration of 1.70 mol/L (E) and 2.55 mol/L (F) (10-μm-thick thin section stained with Congo red; transmission optical microscope). (G–I) PVA-based cryogels (62, Table 1) formed by freezing (−25 °C/12 h) of the aqueous solutions of the polymer without (G) and with the additives of methanol in concentration of 1.23 mol/L (H) and 1.85 mol/L (I) (10-μm-thick thin section stained with Congo red; transmission optical microscope). Note that all these micrographs are from the private archive of the author of the present review and were taken by him personally.

Figure 2

Macroporous morphology of the PVA cryogels prepared by the combination of the cryotropic. gel-formation and the additional phase-transformation processes: (A–C) Respectively, the appearance of the stained with Congo red 2-mm-thick disk (68, Table 1) prepared by freezing (−30 °C/0.5 h and then −5 °C/12 h) of the mixed solution containing PVA (7 wt.%) and gum arabic (7 wt.%) and the optical microscopy images of this gel material under different magnifications. (D–F) PVA-based cryogels (72, Table 1) formed by freezing (−11.6 °C/12 h) of the DMSO solutions of the polymer without (D) and with the additives of methanol in concentration of 1.70 mol/L (E) and 2.55 mol/L (F) (10-μm-thick thin section stained with Congo red; transmission optical microscope). (G–I) PVA-based cryogels (62, Table 1) formed by freezing (−25 °C/12 h) of the aqueous solutions of the polymer without (G) and with the additives of methanol in concentration of 1.23 mol/L (H) and 1.85 mol/L (I) (10-μm-thick thin section stained with Congo red; transmission optical microscope). Note that all these micrographs are from the private archive of the author of the present review and were taken by him personally.

Figure 3

Micrographs demonstrating the influence of different dispersed fillers on the macroporous. morphology of various composite PVA cryogels (all the images were taken using transmission optical microscope for the 10-μm-thick thin sections stained with Congo red): (A) PVA-based composite cryogel (45b, Table 1) formed in a frozen (−20 °C/24 h) aqueous system containing suspended Silasorb−300 silica particles of 5 μm in size. (B) PVA-based composite cryogel (45b, Table 1) formed in a frozen (−20 °C/24 h) aqueous system containing suspended Silasorb-C18 hydophobized silica particles of 7.5 μm in size. (C) PVA-based composite cryogel (50, Table 1) formed in a frozen (−20 °C/12 h) aqueous system containing added tetramethoxysilane, hydrolytic polycondensation of which gave rise to the formation of silica filler particles. (D) PVA-based composite cryogel (69b, Table 1) formed in a frozen (−20 °C/12 h) aqueous system containing PVA and chitosan hydrochloride followed by the in situ transformation of the soluble chitosan salt to the particulate water-insoluble chitosan-base. (E) Microdroplets of the Vaseline oil mechanically dispersed in the aqueous PVA solution. (F) Composite PVA cryogel (56a, Table 1) formed on the basis of above (E) emulsion by its cryogenic processing (−20 °C/12 h). (G–I) Foamed PVA cryogels (49, Table 1) prepared by cryogenic processing (−30 °C/1 h and further −20 °C/23 h) of the following fluid foams: air-whipped aqueous PVA solution (G) foam stabilized with the additives of Brij−56 non-ionic surfactant; and (H) foam stabilized with the additives of CTAB cationic surfactant (I) Note that all these micrographs are from the private archive of the author of the present review and were taken by him personally. CTAB, cetyltrimethylammonium bromide; Brij−56, decaoxyethylene cetyl ether.

Figure 3

Micrographs demonstrating the influence of different dispersed fillers on the macroporous. morphology of various composite PVA cryogels (all the images were taken using transmission optical microscope for the 10-μm-thick thin sections stained with Congo red): (A) PVA-based composite cryogel (45b, Table 1) formed in a frozen (−20 °C/24 h) aqueous system containing suspended Silasorb−300 silica particles of 5 μm in size. (B) PVA-based composite cryogel (45b, Table 1) formed in a frozen (−20 °C/24 h) aqueous system containing suspended Silasorb-C18 hydophobized silica particles of 7.5 μm in size. (C) PVA-based composite cryogel (50, Table 1) formed in a frozen (−20 °C/12 h) aqueous system containing added tetramethoxysilane, hydrolytic polycondensation of which gave rise to the formation of silica filler particles. (D) PVA-based composite cryogel (69b, Table 1) formed in a frozen (−20 °C/12 h) aqueous system containing PVA and chitosan hydrochloride followed by the in situ transformation of the soluble chitosan salt to the particulate water-insoluble chitosan-base. (E) Microdroplets of the Vaseline oil mechanically dispersed in the aqueous PVA solution. (F) Composite PVA cryogel (56a, Table 1) formed on the basis of above (E) emulsion by its cryogenic processing (−20 °C/12 h). (G–I) Foamed PVA cryogels (49, Table 1) prepared by cryogenic processing (−30 °C/1 h and further −20 °C/23 h) of the following fluid foams: air-whipped aqueous PVA solution (G) foam stabilized with the additives of Brij−56 non-ionic surfactant; and (H) foam stabilized with the additives of CTAB cationic surfactant (I) Note that all these micrographs are from the private archive of the author of the present review and were taken by him personally. CTAB, cetyltrimethylammonium bromide; Brij−56, decaoxyethylene cetyl ether.

Figure 4

Schematic diagram showing the applied R&D activities of the research with respect of the developed in IOEC cryogenically-structured materials.