A homologous series of (E)-4-[(4-decyloxyphenyl)diazenyl]phenyl alkanoates (10OABOOCm, m = 1-19) was synthesized and investigated for thermal, structural, and photoresponsive properties. Phase behavior was studied by polarized optical microscopy, differential scanning calorimetry, and thermo-optical analysis. All derivatives exhibited liquid crystalline properties: nematic phase for short chains (m = 1-11), smectic A for two derivatives (m = 1 and 2), smectic C for most compounds (m = 2-19), additional hexatic smectic phases in narrower ranges (SmF: m = 6-13; SmI: m = 9-19), and crystal-like G phase (m = 2-9). X-ray diffraction and Fourier transform infrared spectroscopy confirmed layered packing and characteristic intermolecular interactions, while dielectric spectroscopy revealed relaxation processes in the crystalline phases. UV-vis absorption demonstrated efficient E-Z photoisomerization in solution, with a photostationary state reached within ∼100 s and a rate constant k = 2.81 × 10-2 s-1. These findings show that the terminal chain length influences mesophase formation, molecular organization, and photoresponsivity in this family of azobenzene-based liquid crystals.

Compounds from the group of (E)-4-[(4-octyloxyphenyl)diazenyl]phenyl alkanoates (8OABOOCm, for m = 1–19) were synthesized. The derivatives for m = 2–4 and 7–19 are reported for the first time. The phase behaviour was studied by polarizing optical microscopy, thermo-optical analysis, and differential scanning calorimetry methods. The nematic mesophase was noted for compounds where m = 1–15. The enantiotropic, more organized mesophases, smectic C (m = 5–19), smectic F (m = 8), and G (m = 4–6) phases were also found. In addition, during cooling, smectic F (m = 7, 9–19), G (m = 3, 7–11), and unknown X (m = 4–7) phases were observed. Multiple crystalline phases were noticed in selected derivatives (for m = 1, 2, 4, 5, 7, and 8). The X-ray powder diffraction confirmed the presence of the herring-bone H phase for the 8OABOOC4 compound. The E-Z photoisomerization process was observed for the solution of 8OABOOC7 in response to UV light exposure. A photostationary state was reached after exposure time equal to approximately 90 s. The calculated value of the kinetic constant k was of the order of 10−2 s−1.

Several compounds from the group of (E)-4-[(4-propyloxyphenyl)diazenyl]phenyl alkanoates (3OABOOCm, for m = 1 - 19) were synthesized, with the derivatives for m >= 8 being reported for the first time. The phase situation was investigated by polarizing optical microscopy, thermo-optical analysis, and differential scanning calorimetry methods. The enantiotropic nematic mesophase was noted for compounds where m = 2 - 13, whereas the monotropic nematic phase was observed for m = 1, 14, and 15. Multiple crystalline phase were noticed in selected derivatives (for m = 1 - 3, 9, 13, and 14). The X-ray powder diffraction confirmed the polymorphism of the crystalline phase for the 3OABOOC2 compound. The trans-cis photoisomerization process is attributed to the presence of the diazenyl (azo) group. Absorption spectra, collected as a function of UV light exposure time, indicated a first-order reaction comprising two components. The determined values of the kinetic constant k were of the order of 10-2 s - 1.

Compounds from the homologous series of (E)-4-[(4-heptyloxyphenyl)diazenyl]phenyl alkanoates (7OABOOCm) for m = 1-19, were synthesised. The phase behaviour was investigated by differential scanning calorimetry, polarised light (optical) microscopy, and thermo-optical analysis. The enantiotropic nematic, smectic C and crystal G phases were found for derivatives with m = 1-18, m = 7-17, and m = 4, respectively. In addition, during cooling, smectic F, crystal G, and unknown X phases were observed for derivatives with m = 7-9, m = 3,8,9, and m = 4, respectively. The X-ray diffraction results suggest that the X phase is presumably monotropic crystal H or a second crystal phase. The E-Z photoisomerisation process was observed during UV light irradiation. A photostationary state was reached after exposure time equal to approximately 80 s. The derived kinetic constant k of this process was of the order of 10(-2) s(-1). GRAPHICAL ABSTRACT

Recently, two molecular packing modes of the alkyl chain in smectic A (SmA) liquid crystal phases were revealed: normal and tilted types, which are named by the orientation relative to the layer normal. This study reveals the relationship between the packing mode and thermodynamic order of the SmA-nematic (N) phase transition. Two normal type and three tilted type mesogens were subject to thermodynamic and structural experiments. The DSC results showed that the SmA-N phase transitions of the normal and tilted types are of the second and first order, respectively. The analysis of the intensities of reflections in wide-angle X-ray diffraction related to the periodicity of the SmA layer yielded the distribution of the mass centers of molecules along the normal to the SmA layers. The resultant distribution offered a rationale for the correlation of the thermodynamic order of the SmA-N phase transition and molecular packing modes in the SmA phases based on the Meyer-Lubensky theory.

This publication presents methods of distinguishing the focal texture of the conical smectic phase A (SmA) and the crystalline smectic B phase (CrB). Most often, characteristic transition bars are observed in polarized light at the temperature point of the SmA–CrB phase transition. TOApy software transforms each image from a series of images recorded during POM observation to a function of light intensity versus temperature. Thermo-optical analysis is a powerful quantitative tool to notice this phase transition, but it has some limitations. The other applied method, the local binary pattern (LBP) algorithm, with high probability, detects differences between the textures of the conical focal fan of the SmA and CrB phases. The LBP algorithm is an efficient tool for texture classification.

The k-means cluster analysis has been applied to the temperature-dependent infrared spectra of 4-bromo benzylidene-4'-dodecyloxyaniline (12BBAA). This method appears to be particularly sensitive to the tracking of the melting process of alkyl chains. 12BBAA may form a variety of phases including: isotropic liquid, smectic A, crystalline smectic B and crystal phase. Clustering methods are helpful tool for detection of phase transitions, but do not provide information on the structural changes due to the phase transitions. For this reason, window clustering analysis method has been proposed. Multivariate data has been divided into small spectral windows, and then cluster analysis has been applied for each data window. This approach allows to reduce the dimensionality of large data set, while reveals the spectral characteristic of given phase associated with various regions of spectra. (C) 2021 The Authors. Published by Elsevier B.V.

Many efforts have been made either to provide the typical three-dimensional (3D) printing materials with new and specific properties or to enhance their overall stability. The use of nanomaterials in 3D printing is gaining attention due to the tremendous functionality that this approach provides for those materials. This article presents a method of producing poly(lactic acid) (PLA)-silver nanoparticle antibacterial filament for additive manufacturing. Polymer dope of silver salts within PLA was prepared by the solution-phase and solvent-less methods, followed by extrusion into filaments. Silver nanoparticles were synthesized in situ by thermal decomposition of silver salt during the thermal extrusion of the filament. The formation and dispersion of the nanoparticles within the polymer structure were examined and confirmed with transmission electron microscope and X-ray diffraction. The solution-phase method proposed in this study may prevent failure with nanoparticle dispersion occurring in melt blending. The filament was used for the fabrication of predesigned specimens for antimicrobial and mechanical testing. Printed objects exhibited antimicrobial activity againstStaphylococcus aureus,Escherichia coli, andPseudomonas aeruginosa. This study revealed that the incorporation of silver nanoparticles (0.01-5 wt%) into PLA does not significantly change its bulk properties but renders the composite antibacterial. The filament may be used for manufacturing on-demand customized antimicrobial objects.

Six new compounds were synthesized that have no alkyl chains in their structure: 4-nitrocinnonates of 4-hydroxyazobenzene, 4-nitro-4'-hydroxyazobenzene, 4-fluoro-4'-hydroxyazobenzene, 4-chloro-4'-hydroxyazobenzene, 4-bromo-4'-hydroxyazobenzene and 4-iodo-4'-hydroxyazobenzene. Using the polarizing microscopy and differential scanning calorimetry, enthalpies and temperatures of phase transitions were determined. All investigated compounds have an enantiotropic nematic phase. These compounds proved to be extremely thermally stable. Thermal decomposition was observed in temperatures above 300 degrees C. Investigated compounds contain two different chromophore groups (i.e. azo and ethene moieties), which influenced the complex trans-cis isomerization processes of both groups (three time-separated processes were observed). It was shown that the presence of the ethene group significantly shifts the pi-pi* band towards higher energies. The substituent polarity in the azo group also affected the energy of this absorption band. A weak luminescence effect was observed in the 4-nitrocinnonates of 4-hydroxyazobenzene compound.

Homologous series of esters of (E)-4-[(4-pentyloxyphenyl)diazenyl]phenol and aliphatic carboxylic acids were synthesized, 5O-m for short. Derivatives with alkyl chains longer than seven carbon atoms are described in this article for the first time. The mesogenic properties and phase transition parameters (temperatures and enthalpies) were measured using a polarizing microscopy and a differential scanning calorimetry. Investigated compounds exhibit occurrence of the enantiotropic nematic phase, despite two derivatives with the longest alkyl chains. One can observe two crystalline phases in two derivatives (5O-6, 5O-7). The presence of the azo group in the homologous series of compounds suggests that the possibility of trans-cis isomerization is controlled by light. Such studies have been carried out and their results suggest that the presence of two trans-cis isomerization mechanisms described as the first-order reaction.

The photoisomerization and thermal relaxation processes of three amphiphilic azobenzene derivatives (LCAn) showing liquid-crystalline properties were studied in solutions and in monomolecular films formed using Langmuir and Langmuir-Blodgett techniques. The well-controlled isomeric state of LCAn in chloroform during the UV irradiation allowed to prepare spreading solutions containing trans isomers, cis isomers or their mixture and to investigate molecular organization in the Langmuir films made of them. Surface pressure-mean molecular area isotherms and compression modulus-surface pressure dependences delivered information on a thermodynamic state, phase transitions and intermolecular interaction in the monolayers. LCAn in the trans state create densely-packed films, in which the photoisomerization do not occur due to the lack of free volume for the change of the molecules conformation and their strong tendency for the H-type aggregation. However, the reversible switching of the LCAn conformation during cyclic photoisomerization and thermal relaxation processes was observed in the LB films initially deposited onto quartz substrates in the cis state, where molecules are loosely-packed and exist in the monomeric form. Kinetics and rate constants of the photoisomerization and thermal relaxation were determined based on the recorded absorption spectra in order to obtain information on their efficiency and on the impact of the replacement of the alkyl chain attached in the LCAn para position with the alkyloxy chain. Our research show that LCAn are promising materials for application in optical memories, logic gates and holographic gratings.

Rich polymorphism of ethosuximide compound (ETX) is described in detail using complementary thermal analysis methods. The paper shows as well the results of differential scanning calorimetry (DSC), of polarizing microscope observations (POM) and of X-ray diffraction (XRD) measurements taken using horizontal rotating capillary method. Molecular structure of ethosuximide favors appearance of a conformationally disordered (CONDIS) crystal phase CrI in its polymorphism. Ethosuximide is a good glass former, and glass of the CrI phase was observed even for 5 °C min −1 rate of cooling. Moreover, monotropic plastic crystal CrII phase was observed during heating above the CrI temperature range.

ABSTRACT This paper presents synthesis and liquid-crystalline properties of full homologues series (from acetate to arachidate) of 4-octylphenylazo-4′-phenyl alkanoates. All of the 19 synthesised compounds are liquid crystals with extremely rich mesomorphism. The ester chain length strongly influences mesogenic behaviour of presented materials. In some compounds, up to four liquid-crystalline phases have been observed. There were six different mesophases detected: nematic, smectic C, smectic F, smectic I, J and G. Moreover, some homologues display two crystalline forms. This latter phenomenon does not depend on the ester chain length. Identification of such complicated phase sequences was made based on four methods: polarised light microscopy, thermo-optical analysis, differential scanning calorimetry and X-ray measurements. Graphical Abstract

Chiral high-performance liquid chromatography separation of two recently synthesized liquid crystalline materials C1 and C2 was studied in the reversed-phase mode. Both materials have an azo-moiety and one chiral center in their molecular structures. They were available in racemic and pure S forms. For the enantiomeric separations, a Chiralpak AY-RH stationary phase based on amylose tris(5-chloro-2-methylphenylcarbamate) coated on 5 mu m silica was used. The compounds were analyzed in both of their possible forms, the more thermodynamically stable E form and the labile Z form. The conditions and time scale of the UV-induced E to Z transition were briefly evaluated. Under the optimized conditions, we were able to baseline separate S and R enantiomers of both of the studied materials not only in their E forms, but also in their Z forms. In comparison to the separation in the normal-phase mode, which we have reported recently, the resolution in the reversed-phase mode is significantly better. Interestingly, peak reversal was noticed for the S and R enantiomers when the separation was carried out with E versus Z forms of both compounds.

Observations of the textures and phase transitions of 4-bromobenzylidene-4'-hexyloxyaniline (6BBAA) and 4bromobenzylidene-4'-pentyloxyaniline (5BBAA) thermotropic liquid crystals were carried out using a polarizing optical microscope under crossed polarizers with a hot stage and high -resolution camera. Using open source TOApy software the thermooptical analysis of the phase diagram for 5BBAA and 6BBAA compounds has been obtained without any additional equipment. To obtain thermooptical analysis plot with help of TOApy three different algorithms have been applied. In this manuscript TOApy software is presented as a tool for the detection of phase transitions difficult to observe by DSC method.

Single-crystal structural analyses and heat capacity measurements were performed on two Schiff base liquid crystal compounds, 5CBAA (4-chlorobenzylidene-4'-pentyloxyaniline) and 5ABCA (4-pentyloxybenzylidene-4'-chloroaniline). The alkyloxy-chain of a 5CBAA molecule was conformationally ordered in the crystal at room temperature. While that of 5ABCA was partially disordered in the room temperature phase but ordered in a low-temperature phase at 100 K. The structural phase transition involving the disordering of the conformation was observed at 107 K in the heat capacity of 5ABCA. Both compounds showed two liquid crystalline phases, SmBCr and SmAd. The net entropy change associated with the chain disordering was essentially the same in them despite the difference in the orientation of their central -CH[double bond, length as m-dash]N- moiety. The layer-spacings of SmBCr and SmAd phases were analyzed for their chain-length dependence in both series of mesogens (nCBAA and nABCA), as well as in the case of nBBAA (4-bromobenzylidene-4'-alkyloxyaniline). The results reveal that these smectic structures are composed of alternately stacked core- and chain-layers with an antiparallel arrangement of cores and a bent-form of molecules.

This paper presents synthesis and characterization of new rigid core dye composed of two chromophore moieties such as azobenzene and stilbene parts. During this study liquid-crystalline properties was investigated and found as expected. An additional and unforeseen phenomenon of solid state polymorphism was also noticed. Furthermore, fluorescent properties were examined and confirmed by the fluorescence spectroscopy. This initial study gave very interesting and promising results which can be basis for further studies of such new type of azo-stilbene based substances.

The concept of programmable and reconfigurable soft matter has emerged in science in the last few decades and can be realized by photoisomerization of azobenzene derivatives. This possibility results in great application potential of these compounds in optical storage devices, molecular junctions of electronic devices, command layers of liquid crystal displays or holographic gratings. In this paper, we present the results of a study on the organization and isomerization of the non-ionic and amphiphilic methyl 4-[(E)-2-[4-(nonyloxy)phenyl]diazen-1-yl]benzoate (LCA) in a 2D layer architecture of Langmuir and Langmuir-Blodgett (LB) films supported by spectroscopic studies on LCA chloroform solutions. Our investigation has shown a significantly different molecular organization of LCA depending on the ratio of trans and cis isomers in the monolayers. Taking advantage of a relatively low packing density and aggregation strength in the cis-LCA monolayer, we demonstrated the reversible isomerization in the LB film initially formed of LCA molecules in the cis form, while in the trans-LCA monolayer this effect was not observed. Our approach allows the formation of a switchable monolayer made of the amphiphilic LCA showing liquid crystalline properties without introducing an ionic group into the molecule structure, mixing with another compound or changing the subphase pH to provide free space for the molecules' isomerization.