Flexible Siloxane Research Articles

Effect of the Type of a Cross-Linking Agent on the Swelling Degree of Polydecylmethylsiloxane

In this work, the effect of the type of a cross-linking agent for polydecylmethylsiloxane (C10) on its sorption and swelling in organic solvents was studied for the first time using toluene, octane, isooctane, and butyl acetate. Hydrocarbon (1,7-octadiene (OD), 1,9-decadiene (DD), 1,11-dodecadiene (DdD)), vinyl-terminated PDMS (Mn = 500 g/mol (Sil500), Mn = 25000 g/mol) and combined cross-links were used for membrane obtaining. It was shown that cross-linking with hydrocarbons leads to the least swelling in the solvents explored, while cross-linking with vinyl-terminated PDMS results in the greatest swelling. Apparently, the flexible siloxane cross-linking imparts greater mobility to C10, which leads to high absolute sorption values. At the same time, the rigid hydrocarbon cross-linking allows the formation of a structure specific to the comb-shaped polymer, which significantly contributes to its properties.

Constructing high-toughness polyimide binder with robust polarity and ion-conductive mechanisms ensuring long-term operational stability of silicon-based anodes

Silicon-based materials have demonstrated remarkable potential in high-energy–density batteries owing to their high theoretical capacity. However, the significant volume expansion of silicon seriously hinders its utilization as a lithium-ion anode. Herein, a functionalized high-toughness polyimide (PDMI) is synthesized by copolymerizing the 4,4′-Oxydiphthalic anhydride (ODPA) with 4,4′-oxydianiline (ODA), 2,3-diaminobenzoic acid (DABA), and 1,3-bis(3-aminopropyl)-tetramethyl disiloxane (DMS). The combination of rigid benzene rings and flexible oxygen groups (-O-) in the PDMI molecular chain via a rigidness/softness coupling mechanism contributes to high toughness. The plentiful polar carboxyl (–COOH) groups establish robust bonding strength. Rapid ionic transport is achieved by incorporating the flexible siloxane segment (Si-O-Si), which imparts high molecular chain motility and augments free volume holes to facilitate lithium-ion transport (9.8 × 10−10 cm2 s−1 vs. 16 × 10−10 cm2 s−1). As expected, the SiOx@PDMI-1.5 electrode delivers brilliant long-term cycle performance with a remarkable capacity retention of 85% over 500 cycles at 1.3 A g−1. The well-designed functionalized polyimide also significantly enhances the electrochemical properties of Si nanoparticles electrode. Meanwhile, the assembled SiOx@PDMI-1.5/NCM811 full cell delivers a high retention of 80% after 100 cycles. The perspective of the binder design strategy based on polyimide modification delivers a novel path toward high-capacity electrodes for high-energy–density batteries.

Non-Isocyanate Poly(Siloxane-Urethanes) Based on Oligodimethylsiloxanes Containing Aminopropyl and Ethoxy Substituents

Environmentally friendly method for the synthesis of crosslinked poly(siloxane-urethanes) avoiding the use of toxic isocyanates has been presented. The synthesis has been performed in two stages: at the first stage, non-isocyanate poly(siloxane-urethanes) have been synthesized via aminolysis of cyclocarbonates (differing in the structure and functionality) with oligomer dimethylsiloxanes bearing aminopropyl and ethoxy substituents, and crosslinked non-isocyanate poly(siloxane-urethanes) have been obtained via hydrolysis of the ethoxy groups with air moisture. According to the TGA data, processes of thermooxidative decomposition of the non-isocyanate poly(siloxane-urethanes) begin at 240‒260°C, depending on the structure of the organic block. Structural organization of the films has been investigated and glass transition temperature of two blocks (flexible siloxane and rigid urethane ones) has been determined by means of DSC and TMA. Surface of the film samples of non-isocyanate poly(siloxane-urethanes) has been assessed by means of scanning electron microscopy.

Development of 3D Printable Highly Flexible Siloxane Elastomers for Direct Ink Writing (DIW) of Soft Robotic Actuators for Space Applications

There is an interest in soft robotics for various space applications within low gravity and tight space environments to navigate, observe and even service various components within space assets, spacecraft and planetary stations. As an example, in an emergency, such as a pipe system failure occurring in a spacecraft, a soft robot may be able to assist in navigating the structure to detect the location and means of failure. The manufacturing of soft robotic actuators in space can be crucial. In addition, the fabrication of soft robotic tooling in a single step plays a critical role in space. 3D printing systems allow the manufacturing of soft robotic actuator parts in a single step. Stereolithography (SLA) and digital light processing (DLP) systems are not convenient because of the space environment. However, direct ink writing (DIW) which is the most commonly available and affordable system compared to SLA or DLP can be utilized to produce 3D objects, in addition, the DIW process permits the ability to in situ produce composite structures during the printing process. Various inorganic particles can be inserted within the elastomer print to control the mechanical, electrical and magnetic properties on-demand to produce smart or multi-functional soft robotic actuators and structures.The current work focuses on the development of a highly flexible and low (or nearly no) cytotoxicity silicone-based elastomer via thiol-ene click reaction that allows rapid polymerization of an elastomer to prevent the collapse of the structure during the printing. The work also demonstrates the use of this novel UV-durable elastomer to produce structures with embedded electrical interconnects and sensors for in-situ measurement of temperature and strain. In this study Poly(mercaptopropylmethylsiloxane-co-dimethylsiloxane) (M-MPS) was first prepared through the cohydrolysis-condensation reaction of 3-Mercaptopropylmethyltrimethoxysilane (MPS) and dimethyldimethoxylsilane (DMDES) with water and hydrochloric acid. Then M-MPS was compounded with various molecular weight vinyl-terminated polydimethylsiloxane (VPS) (MW~800-25000) and different dosage (0.1- 4.0 wt%) of a photoinitiator (1:1 weight ratio of 2-Hydroxy-2-methyl-phenyl-propane-1-one (PI 1173) and phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide (PI819)). For example, Figure 1 depicts the change in the viscosity of (M-MPS)-VPS 6000 2 wt% when it exposes to UV light irradiation. When (M-MPS)-VPS 6000 2 wt% was exposed to UV light irradiation, it polymerized at ~2 sec which is enough time to retain the structure during printing. To elucidate the properties of synthesized elastomer, FTIR, NMR, SEM, and tensile test measurements were performed. Furthermore, the synthesized elastomer was loaded with conductive inorganic particles so as to utilize the printed material as a temperature and tactile sensor (and sensor array). In addition, other printing variables were evaluated to produce 2D/3D structures of the pure and composite elastomers, such as the effect of the power and wavelength of UV light source, loading different types of conductive powders, and thiol-ene ratio. Acknowledgments: Work supported by a subcontract under the NASA-EPSCOR program (project number is 80NSSC20M0218). The authors would like to thank our NASA technical monitor Mr. Curtis Hill and project manager Dr. Melanie Page due to their contributions. Material characterization and imaging work were made possible with the support of the West Virginia University Shared Research Facilities (SRF). Figure 1

Hierarchically Branched Siloxane Brushes for Efficient Harvesting of Atmospheric Water.

Atmospheric water harvesting is considered a viable source of freshwater to alleviate water scarcity in an arid climate. Water condensation tends to be more efficient on superhydrophobic surfaces as the spontaneous coalescence-induced droplet jumping on superhydrophobic surfaces enables faster condensate removal. However, poor water nucleation on these surfaces leads to meager water harvest. A conventional approach to the problem is to fabricate micro- and nanoscale biphilic structures. Nonetheless, the process is complex, expensive, and difficult to scale. Here, the authors present an inexpensive and scalable method based on manipulating the water-repellent coatings of superhydrophobic surfaces. Flexible siloxane can facilitate water nucleation, while a branched structure promotes efficient droplet jumping. Moreover, ToF-SIMS analysis indicated that branched siloxane provides a better water-repellent coating coverage than linear siloxane and the siloxanes comprise hydrophilic and hydrophobic molecular segments. Thus, the as-prepared superhydrophobic surface, TiO2 nanorods coated with branched siloxanes harvested eight times more water than a typical fluoroalkylsilane (FAS)-coated surface under a low 30% relative humidity and performed better than most reported biphasic materials.

Novel liquid phthalonitrile monomers towards high performance resin

Phthalonitrile resins are one of the high temperature resistant polymers which can be potentially used for harsh environments in both military and domestic fields. The high melting points of the monomers led to short processing windows and made processing procedure challenging and energy intensive. To solve this problem, liquid phthalonitrile monomers containing flexible siloxane segments were designed and synthesized. The long bond length and large bond angle of Si-O-Si chain segments introduced flexibility into the monomers and effectively reduced the melting point to −35.9 °C. Meanwhile, the high bond energy preserved the thermal stability of the resulting cured resin. The high fluidity (viscosity of ∼ 2 Pa·s at 30 °C) allows the monomers to be processed at room temperature without additional heating. In addition, the monomers can be dissolved in common organic solvents, such as ethyl acetate and ethanol. The resins cured at 250 °C demonstrated good thermal and thermal oxygen stability. The weight loss of 5 % in argon and air at temperatures of 428.6 °C and 434.9 °C, respectively. Furthermore, blending this liquid monomer blended with powdered monomers improved both the processibility of the high melting monomers and the overall temperature resistance of the cured resin. The resin showed a weight loss of 5 % in argon and air of 534.4 °C and 532.3 °C, respectively.

Preparation of phthalonitrile resins containing siloxane linkages with improved processability

To improve the processability of biphenyl phthalonitrile resin, a flexible siloxane structure was introduced into the phthalonitrile monomer through molecular design, which was then blended with a biphenyl monomer to prepare phthalonitrile alloy resins. When the ratio of phthalonitrile monomer containing flexible siloxane to biphenyl phthalonitrile monomer was 1:1, the processing window widened from 58 to 110°C, as compared to that of biphenyl phthalonitrile. Due to the introduction of the biphenyl structure into the phthalonitrile alloy resins, the initial decomposition temperature of the silicon-containing phthalonitrile resin increased from 385 to 516°C. More importantly, the phthalonitrile alloy resin exhibited a high bending strength (66 MPa) and bending modulus (3762 MPa), indicating that it could be potentially applied as high temperature structural composite matrices. Furthermore, it provides a new strategy for processing phthalonitrile resins with a high melting point and narrow processing window.

Novel photosensitive resin simultaneously with outstanding cryogenic strength and toughness for digital light processing three-dimensional Printing

With the increased demand for three-dimensional (3D) printing technology in various fields, it is important to develop high-performance resin that could withstand temperature changes to expand their application potential. A new photosensitive oligomer (BDM–DDM–ETPS–GMA) based on epoxy-terminated polyether siloxane (ETPS) and bismaleimide diphenylmethane/4, 4′-diaminodiphenylmethane (BDM–DDM) resin was synthesized and then mixed with other oligomers, reactive diluents, and photoinitiators to prepare a novel 3D printing resin. The results show that the resulting resins exhibit good fluidity and rapid photopolymerization ability, which satisfies the rheological prerequisites of 3D printing resin. Moreover, the incorporation of BDM–DDM–ETPS–GMA can simultaneously improve the cryogenic stiffness and toughness of commercial resin. Specifically, the tensile strength, elongation at break, flexural strength, impact strength, and storage modulus at −30 °C of modified resin with 15% BDM–DDM–ETPS–GMA are 151.2 MPa, 10.9%, 146.2 MPa, 9.8 kJ/m2, and 4,131 MPa, respectively, which are about 2.81, 1.70, 1.37, 1.81, and 1.54 times of that of commercial resin. A synergistic enhancement mechanism is believed to be attributed to these results, which includes the introduced flexible siloxane chain and the rigid bismaleimide structure as well as decreased cross-linking density. These attractive features of modified resins suggest that the method proposed herein is a new approach to develop high-performance 3D printing photosensitive resin simultaneously with outstanding cryogenic strength and toughness and thus has wide application potential in the aerospace, military industry, and other cutting-edge fields.

Portable wireless humidity sensor based on hyperbranched polysiloxane for multifunctional non-contact sensing

Non-contact sensing is an immediate research focus as a much greener and hygienic human-machine interface. Nonetheless, much research remains to be done on fast and stable non-contact sensors based on humidity signals. Hence, in this paper, hyperbranched sulfonated polysiloxane (HPS) with carboxyl groups at the end was synthesized by polycondensation reaction. The resulting polymer was compounded with LiCl and fabricated into humidity sensors. Benefiting from the tailored hydrophilicity/hydrophobicity of the material, flexible siloxane backbones and ionized LiCl, the sensor exhibited five orders of magnitude impedance changes over a wide humidity test range (11–98% RH) with rapid response (1–2 s) and small humidity hysteresis (3% RH). The results of continuous cyclic test confirmed the good reproducibility and stability of the material. Moreover, the sensor was able to distinguish and respond to fingers at different distances, respirations with altered frequencies and various commands. By integrating humidity sensors into the circuit, a low-cost, portable and wireless non-contact monitoring device was developed. The detector enables real-time display of data on a cell phone, which is of great potential value for non-contact distance detection, command recognition and respiration monitoring.

Adhesion and Interface Studies of the Structure‐Controlled Polyimide with Smooth Copper for High‐Frequency Communication

AbstractFan‐out wafer‐level packaging (FOWLP) is expected to become the dominating trend in millimeter wave and 5G communication. However, the reliability faces enormous challenges due to the inherent poor adhesion between the insulating layer of polyimide (PI) and copper wirings in FOWLP. Herein, adhesive polyimide (API) with improved adhesion on smooth Cu by the introduction of benzimidazole and siloxane structure is reported. The results prove that the adhesion strength is increased by 191.46% compared with the conventional PI, owing to the generation of Cu complexes by benzimidazole as well as the cooperation of the flexible siloxane segments. Besides, the APIs not only hold a proper coefficient of thermal expansion (CTE) of 6.28 × 10−6 K−1 matching with Si wafers (2.5 × 10−6 K−1), but also possess CTE (18.56 × 10−6 K−1) of API‐3 matching with Cu circuits (17 × 10−6 K−1), so that a low residual stress of −1.849 MPa is obtained. Moreover, superior mechanical, thermal properties are also obtained, of which the modulus and tensile strength are 6.31 GPa and 170 MPa, while Tg and T5% are as high as 474.6 and 524.57 °C, respectively. Therefore, the as‐prepared high‐performance APIs can be prospective candidates in FOWLP for high‐frequency communication.

Fast Photoswitchable Order-Disorder Transitions in Liquid-Crystalline Block Co-oligomers.

Optically driven ordering transitions are rarely observed in macromolecular systems, often because of kinetic limitations. Here, we report a series of block co-oligomers (BCOs) that rapidly order and disorder at room temperature in response to optical illumination, and the absence thereof. The system is a triblock where rigid azobenzene (Azo) mesogens are attached to each end of a flexible siloxane chain. UV-induced trans-to-cis Azo isomerization, and vice versa in the absence of UV light, drive disordering and ordering of lamellar superstructures and smectic mesophases, as manifested by liquefaction and solidification of the material, respectively. The impacts of chemical structure on BCO self-assembly and photoswitching kinetics are explored by in situ microscopy and X-ray measurements for different mesogen end groups (NO2 or CN), and different carbon chain lengths (0C or 12C) between the siloxane and the mesogen. The presence of the 12C spacer leads to hierarchical ordering with smectic layers of mesogens existing alongside larger length-scale lamellae, versus only smectic ordering without the spacer. These hierarchically ordered BCOs display highly persistent lamellar sheets that contrast with the tortuous, low-persistence "fingerprint"-type structures seen in conventional block copolymers. The reordering kinetics upon removal of UV illumination are extremely rapid (<5 s). This fast response is due to the electron-withdrawing NO2 and CN, which facilitate cis-to-trans isomerization via thermal relaxation at room temperature without additional stimuli. This work elucidates structure-property relationships in photoswitching BCOs and advances the possibility of developing systems in which ordered nanostructures can be easily optically written and erased.

Biomass-derived dynamic covalent epoxy thermoset with robust mechanical properties and facile malleability

Biomass-derived dynamic covalent thermoset has been considered as a promising solution to the high dependence on fossil resources and the difficulty in recyclability after curing of conventional bisphenol A epoxy resins. However, the design and preparation of a dynamic covalent biobased epoxy thermoset with both comparable thermal and mechanical performances to bisphenol A epoxy resins and reprocessibility remains a significant challenge. Herein, based on imine chemistry, a novel Schiff base-containing dynamic covalent epoxy thermoset was facilely fabricated from biobased protocatechualdehyde and synthetic siloxane diamine. Due to the more reactive epoxides in the epoxy monomer than in bisphenol A epoxy oligomer, the thermoset exhibited a high cross-linking density, resulting in high thermal stability and glass transition temperature. The rigid aromatic Schiff base moieties endowed the thermoset with excellent mechanical properties: Thanks to the plasticization of the flexible siloxane, the thermoset displayed high impact strength. Meanwhile, owing to the high segmental mobility, the fast exchange of imine bonds was guaranteed; and the thermoset was able to be recycled through reprocessing. Taking these features, this work provided great potential for designing and preparing sustainable substitutes for bisphenol A epoxy resins in the high-performance applications.

Improvement of oxygen permselectivity of a rigid helical polyphenylacetylene: Effect of flexible groups, degree of polymerization, composites, thickness, orientation, and network formation

In order to improve oxygen permselectivity of a rigid helical poly(alkenylphenylacetylene) membrane having a columnar liquid crystalline structure, several chemical and membrane structures including the degree of polymerization and the orientation of the macromolecules were modified and controlled. Introduction of longer alkenyl or flexible siloxane groups significantly enhanced oxygen permeability (PO2) and by reducing the degree of polymerization and the thickness of the membranes, or by the formation of network structures oxygen permselectivity (α = PO2/PN2) was effectively enhanced. The membranes from polymers with very small degree of polymerization and perpendicular orientation had extremely high α. In spite of the membranes from the polymers having the identical chemical structure, their performances could be optimized by controlling several membrane structures.

UV-Resistant Trifluoropropyl-Substituted Open-Cage Silsesquioxane-Pendant Polysiloxanes

We prepared three types of tris(dimethoxysilyl)-heptatrifluoropropyl-substituted open-cage silsesquioxanes, namely hepta(3,3,3-trifluoropropyl)-substituted open-cage silsesquioxanes (IC-POSSs) attached to three dimethoxysilyl groups by linkers of variable lengths at the opening vertex (TFP-Hdi, TFP-Vdi, and TFP-Adi). The dimethoxysilyl groups allowed subsequent hydrolysis and polycondensation under mild conditions to form flexible siloxane bonds. The structures of the resulting trifluoropropyl-substituted open-cage silsesquioxane-pendant polysiloxanes (P-H, P-V, and P-A) could be tuned by polycondensation temperature and the linker lengths of the tris(dimethoxysilyl)-heptatrifluoropropyl-substituted open-cage silsesquioxanes. The hybrid structure of the trifluoropropyl-substituted open-cage silsesquioxane-pendant polysiloxanes exhibited a low glass transition temperature, good thermal stability, hydrophobicity, optical transparency, and ultraviolet (UV) resistance. In particular, the transmittance of P-H exhibited no significant changes even after 11 days of UV irradiation with an average transmittance of >90% (250–600 nm). On the other hand, the transmittance of sulfur-containing P-V and P-A initially decreased after 2 days of irradiation due to oxidation of sulfur atoms to sulfoxide. Sulfoxide presence was then validated by XPS measurements. However, the transmittance remained largely unchanged during further consistent irradiation, indicating no further changes.

Siloxane tethered perylene diimide: from monotropic phase structures to tunable photoconductivity

PDI-TTMSS exhibits peculiar monotropic phase transition behaviors originated from flexible siloxane substituents.

Synthesis of New of Norbornene–1,5-Bis(hexenyl)hexamethyltrisiloxane Copolymers via Olefin Metathesis Reaction

New copolymers of norbornene and 1,5-bis(hexenyl-5)-1,1,3,3,5,5-hexamethyltrisiloxane containing flexible siloxane and rigid norbornene fragments in the main chain are synthesized. Synthesis is carried out using three types of olefin metathesis reactions: the ring-opening metathesis polymerization of norbornene, the metathesis of nonconjugated diene 1,5-bis(hexenyl-5)-1,1,3,3,5,5-hexamethyltrisiloxane, and the interchain macromolecular cross-metathesis between polynorbornene and siloxane-containing polyene. The latter reaction is studied for the first time. With its help, new statistical multiblock copolymers of norbornene and 1,5-bis(hexenyl-5)-1,1,3,3,5,5-hexamethyltrisiloxane with different average block lengths are obtained and characterized by 1H and 13C NMR and IR spectroscopy. The effect of the copolymer structure on their thermal properties is investigated.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.

Synthesis and properties of new dibenzoylmethanatoboron difluoride dyads connected by flexible siloxane linkers

A series of novel dibenzoylmethanatoboron difluoride (DBMBF2) and methoxy-substituted DBMBF2 dyads linked via flexible dimethylsiloxane linkers of variable length were synthesized and characterized. Both monomer and excimer (trough intramolecular excimer formation) emissions are observed for the dyads in dilute dichloromethane solutions at room temperature. The excimers contribution into the total fluorescence spectrum decreases with increasing siloxane linker length. The parallel-sandwich conformation of intramolecular pre-excimers formed by two terminal DBMBF2 moieties is confirmed by DFT-based calculations.

Exploring ion-ion preferences through structure-property correlations: amino acid-derived, bis(guanidinium) disiloxane salts

In a more synthetical approach to the study of ion-specific phenomena, four dipodal bis(guanidinium) siloxanes have been synthesized starting from glycine, β-alanine, γ-aminobutanoic acid, L-proline and 1,3-bis(3-aminopropyl)tetramethyldisiloxane. Together with their non-amide progenitor they were comparatively studied in regards to their interactions with nine different anions: sulphate, chromate, molybdate, benzoate, chloride, azide, nitrite, nitrate and thiocyanate. Their aqueous solubilities, form, 1H NMR and FT-IR spectra were examined while searching for anion-specific interactions falling in- or outside of the Hofmeister series. We show that although the “chao-” and “kosmotropic” ions affect the properties of solutions in a predictable way, more selective cation-anion pairing is responsible for phase separation and crystallinity. As a prominent example, crystal structure of one of the benzoate salts was successfully obtained and reveals a synergy of hydrophobic packing, ionic and hydrogen bonding. Immobilized but still flexible siloxane bridges give rise to crystals described by P 42/n space group and neatly segregated into hydro- and lipophilic sections.

Molecular design of anti-spindle-like molecules by use of siloxanyl terminals for a thermotropic bicontinuous cubic phase.

Selecting 1,2-bis(aryloyl)hydrazine as a model molecular framework, this article examines how the combined modification of two molecular moieties, i.e., variation of the molecular core motif (benzene B or naphthalene N as two aromatic rings) and use of bulky and flexible siloxane segments (disiloxane Si2, trisiloxane Si3, or its branched type iSi3) at the end of both chains, affects the phase behavior including the cubic (Cub) phases such as well-known achiral Ia3d or the so-called "Im3m" phase mostly recognized as a chiral one. It was found that the use of a naphthalene core as a larger core effectively provides the compound with improved thermal stability, and the clearing temperature in the N series is ca. 50 K higher than that of the B series. On the other hand, the introduction of siloxane segments at their terminals is effective for lowering the LC-phase temperature range by several tens of K. Focusing on the Cub phases, only the introduction of the disiloxane Si2 segment was useful for their formation, and we envisioned how much degree the anti-spindle shape of the average molecular shape is in the Ia3d phase. The use of the trisiloxane Si3/iSi3 segment primarily led to the formation of columnar (Col) phases. Consideration of the chemical composition revealed that the delicate balance between the three molecular moieties, siloxane terminal, alkyl spacer, and aromatic core part, is critical for the Cub phase formation, and it can be summarized as the threshold weight fraction of the alkyl spacer in the three moieties being 0.284 or larger, which derives an anti-spindle shape favorable for the formation of the Ia3d-Cub phase.