Structure Memory Effect Research Articles

Shape memory effects of poly(L-lactide) and its copolymer with poly(ε-caprolactone)

The thermal properties, crystalline structure and shape memory effects of poly(L-lactide) (PLLA) and its copolymer with poly(e-caprolactone) (PCL) are systematically investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tensile tests. The influences of composition and intrinsic viscosity on structure and shape memory effects are also revealed. It is found that the PLLA homopolymer and poly(L-lactide-co-e-caprolactone) (PCLA) copolymers exhibit good shape memory effects. The existence of PLLA crystal and amorphous phase play very important roles for shape memory effects. The intrinsic viscosity obviously affects the crystallinity of polymers and further affects the shape memory effects. The shape recovery rate decreases with increasing deformation strain, which is relate to the deformation of PLLA crystal. The recovery stress increase with the increase of the e-CL content and maximum recovery stress is 3.54MPa obtained in the PCLA804 (20wt% e-CL content, Mw=304,400). With the increase of cyclic testing number, the shape recovery rates decrease and the shape retention rates increase at the beginning and then approach to a steady value.

STUDIES ON MORPHOLOGY AND PROPERTIES OF PHMA LIQUIFIED MDI/BDO SHAPE MEMORY POLYURETHANES (PU)

Segmented polyurethanes,Poly(hexamethylene adipate)/liquified 4,4′-methylenedi(phenylisocyanate)(L-MDI)/butanediol(PHMA/L-MDI/BDO) were prepared by a two-step process,and their structure and shape memory effect were investigated by DSC、WAXD testing,the tensile mechanical,dynamical mechanical properties were discussed also in this paper.It was found that the hard segment regions of these PUs were amorphous,and the soft segment ones were crystalline.The samples exhibited obvious shape memory behavior with shape recovery temperature around 35～45℃.The strain fixity was close to 100%,and the maximum shape recovery rate was more than 97%.The sample showed high tensile strength,28～(50?MPa),and large elongation at break,900%～1400%,at room temperature.Dynamic mechanical tests indicated that the modulus at room temperature was about 140 times as high as that in the rubbery platean region,it shown an excellent dynamical property.

Shape memory effect of PU ionomers with ionic groups on hard-segments

SMPU (shape memory polyurethane) non-ionomers and ionomers, synthesized with poly(e-caprolactone) (PCL), 4, 4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), dimethylolpropionic acid (DMPA) were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA con...

A study of structural memory effects in synthetic hydrotalcites using environmental SEM

The ‘memory’ effect in synthetic hydrotalcite was demonstrated using d(001) and d(002) peaks in X-ray diffraction (XRD) patterns. These peaks were present in the hydrotalcite before it was calcined and after it was reformed but not in the thermally activated hydrotalcite. SEM images were taken of the hydrotalcite to show the layering and size of the crystals. Environmental SEM (ESEM) images were taken of the thermally activated hydrotalcite, and then manipulation of temperature and pressure allowed water to condense on the sample. The ESEM images show that the layered structure is reforming following exposure to water.

Utilizing the structural memory effect of layered double hydroxides for sensing water uptake in organic coatings

In this paper, we report results demonstrating the structural memory effect of synthetic calcined layered double hydroxide (LDH) Li 2[Al 2(OH) 6] 2CO 3· nH 2O powder immersed in a bulk electrolyte, exposed to humid air, and embedded in a water-permeable epoxy matrix. Reconstruction of calcined LDH by the structural memory effect can be detected by X-ray diffraction (XRD) leading to a novel approach for remotely and non-destructively detecting water uptake in optically opaque organic coatings. The LDH Li 2[Al 2(OH) 6] 2CO 3· nH 2O was synthesized by aqueous co-precipitation then calcined in air at temperatures in excess of 220 °C to form a Li–Al mixed hydrated oxide powder. Reconstruction in a matter of days was observed when the calcined mixed oxide was immersed in 0.5M NaCl solution. During exposure to humid air, LDH reconstruction was slower occurring over a matter of weeks, perhaps in a deliquescent electrolyte. Paint-like coatings were made and applied to aluminum alloy 2024-T3 (Al–4.4Cu–1.5Mg–0.6Mn) substrates by adding the calcined LDH at a rate of 10 wt.% to a commercial epoxy. Coated substrates were then exposed to 0.5M NaCl solution and LDH reconstruction progressed over tens of days as the coating absorbed water. During these exposure experiments, XRD and electrochemical impedance spectroscopy measurements were made periodically to track LDH reconstruction and measure uptake of water in the coating via capacitance measurements. LDH reconstruction was tracked using the ratio of the {0 0 3} LDH diffraction peak to the {1 1 1} Al diffraction peak. Using the Brasher–Kingsbury equation, the volume fraction of water in the coating was estimated from capacitance data. Up to the point of apparent coating saturation (about 10 vol. %), the XRD peak height ratio varied linearly with the estimated coating water content. This result suggests that additions of calcined LDH to organic coating may lead to methods for sensing early-stage coating degradation due to water uptake and may give an advance warning of substrate corrosion.

Protonated Benzene: A Case for Structural Memory Effects?

Photoionization tandem-mass spectrometry of selectively deuterium labeled precursor molecules is used to probe the structure of protonated benzene which had been questioned in a provocative publication by Mason and co-workers (J. Chem. Soc., Chem. Commun. 1995, 1027). Specifically, we address the intriguing aspect of a postulated delayed hydrogen ring-walk by modulating the internal energy content of mass-selected C6H7-nDn+ ions. To this end, ionization of selectively deuterated precursors by tunable synchrotron photons is combined with chemical monitoring of H+/D+ transfer from C6H7-nDn+ to a strong base B. The resulting BH+/BD+ ratios monotonically decrease with increasing internal energy content and, due to the virtue of the regioselective deuterium label incorporations, thereby disprove a delayed hydrogen ring-walk or any other “structural memory effect” in C6H7-nDn+ ions. As a consequence, the experimental studies of Mason et al. were reconsidered using sector-field mass spectrometry. These extensive studies suggest that the previous observations might have been obscured by a combination of isobaric impurities, metastable-ion contributions, and artifact signals.

Relation between structure, magnetization process and magnetic shape memory effect of various martensites occurring in Ni-Mn-Ga alloys

Magnetic properties and magnetic shape memory effect of three Ni-Mn-Ga alloys representing three different martensitic phases; five-layered tetragonal (5M), seven-layered orthorhombic (7M), and non-modulated tetragonal (NM) martensite were studied at room temperature. Magnetization process occurs mostly by magnetization rotation. Magnetic anisotropy energy is high for all three phases ranging from 1.1 to 1.7×10 5 J/m 3 . The direction of short lattice constant is always a direction of easy magnetization. It is demonstrated that the high magnetic anisotropy and low twinning stress render a MSM effect possible in 5M and 7M martensite. The 5M martensite exhibits more than 6% field induced strain. The giant strain is followed by large magnetization jump. Simultaneous measurement of magnetization changes and field-induced strain as a function of magnetic field demonstrates the nature of the magnetic shape memory effect and validates the proposed mechanism.

Reversible phase transition and structure memory effect of metastable phase in electron-irradiated poly(vinylidene-fluoride-trifluoroethyline) copolymers

We report the results of x-ray diffraction studies on phase transition behavior of irradiated poly(vinylidene-fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer. It is found that the transformations between the polar ferroelectric phase, the metastable paraelectric phase, and normal paraelectric phase induced by thermal and electric field are reversible. The reversible phase transition of the metastable paraelectric phase is very important to explain the appearance of giant strain in the irradiated P(VDF-TrFE) copolymer. The macroscopic strain caused by these reversible transitions was estimated.

Probing Porous Polymer Resins by High-Field Electron Spin Resonance Spectroscopy

High-field W-band (95 GHz) electron spin resonance spectroscopy of various spin probes was used to study the structure of highly cross-linked porous polymer resins based on a styrenedivinylbenzene matrix. The pores of these resins were created by template imprinting with reverse micelles solubilized in the mixture of monomers and cross-linkers prior to the polymerization. Functional groups in the resins were introduced by the use of polymerizable cosurfactants in the reverse micelles. Sufficiently large unpolar spin probes exhibit a distribution of mobilities that can be attributed to regions with different degrees of cross-linking in the polymer. The dynamics of a surfactant spin probe is sensitive to the presence of pores and the functionalization of the pore surface with highly polar groups. This effect disappears when the headgroup of the surfactant spin probe is esterified. It can be considered as a structural memory effect related to the use of reverse micelles as templates for imprinting. The result indicates that the pores can be filled or washed selectively.

Structural reversibility of a ternary CuO–ZnO–Al2O3 ex hydrotalcite-containing material during wet Pd impregnation

A Cu-Zn-Al precursor was synthesized by coprecipitation of the corresponding cations with sodium carbonate at constant pH and temperature. CuO-ZnO-Al2O3 composite oxide support was obtained by calcination (673 K) of the Cu-Zn-Al precursor. Two palladium-modified CuO-ZnO-Al2O3 samples were prepared by impregnation of the mixed-oxide support and further calcination (673 K). The presence of remaining CO32- anions in the CuO-ZnO-Al2O3 mixed oxide, as a result of incomplete Cu-Zn hydrotalcite phase decomposition, and the hydrothermal-like treatment during the Pd impregnation step, allow the partial reconstruction of the Cu-Zn hydrotalcite-type structure (memory effect). In addition, an enhancement in the CuO crystallinity was obtained for the Pd-modified oxides. A detailed characterization revealed that the hydrotalcite restoration enhances the crystallinity of the copper oxide as a consequence of a crystalline rearrangement of this oxidic phase.

Transformation temperatures, elastic and anelastic properties of Cu-Al-Ni crystals subjected to impact loading

Experimental investigations of the influence of impact loading on properties of Cu-Al-Ni single crystals have been performed. Crystals in the β 1 phase were impacted with pulses of a uniaxial plane strain wave with a duration of about 2×10 -6 s. A normal component of stress in the direction of the pulse propagation ranged from 0.5 to 5.4 GPa. For as-quenched and impacted crystals martensitic transformation temperatures were determined, the Young's modulus (YM), strain amplitude-independent and strain amplitude-dependent internal friction were measured at a frequency of about 100 kHz over the temperature range of 300-90 K for strain amplitudes of 10 -7 -2×10 -4 , Experimental results indicate that β 1 →γ 1 ' martensitic transformation (MT) and plastic deformation of the martensite are induced by the impact. The impact loading generates a « structure memory effects: the YM in the austenite is not sensitive to the impact, but the consequent temperature-induced MT reveals a dramatic influence of the impact on the YM of the γ 1 ' martensite. The conclusion is drawn that the observed effect is fundamentally similar to the two-way memory effect, but is extremely sensitive to the impact stress. The origin of this phenomenon is attributed to the internal stresses, created by impact, which control the nucleation of preferentially oriented anisotropic martensitic variants during temperature-induced MT in impacted crystals. No influence of the impact loading on the transformation temperatures was detected for β 1 →γ 1 ' MT, in contrast to elastic properties of the martensitic phase, indicating that structural changes due to the high-velocity impact do not affect appreciably the thermoelastic equilibrium and hysteretic motion of parent- martensite boundaries during the MT.

Optimization of the Positive Active Material Capacity in Lead‐Acid Cells Through Control of the Basic Lead Sulfate Precursor

The mechanisms for the (denoted 3BS) → and (denoted 4BS) → transformations were studied from well‐defined, pure samples formed in a laboratory cycling test cell. The oxidation reactions were observed using X‐ray diffraction and scanning electron microscopy (SEM). No structural memory effect was found between 3BS and since the 3BS → reaction occurred through a dissolution recrystallization process. In contrast, textural relationships between needle‐shaped 4BS and were evidenced by SEM analyses. Indeed, 4BS was found to transform into , which in turn transformed into while retaining the needle shape as long the reaction proceeded. The thickness of the needle crust surrounding the 4BS needle core was found to depend on both the temperature and soaking duration. A model predicting a decrease in the capacity with the increase in the needle thickness, as a consequence of the inactive 4BS presence inside the needles, is proposed. The ability to prepare samples of controlled morphology revealed a decrease in capacity with the increase in the needle thickness, thereby confirming the model prediction. But more importantly, we showed that a 20–25% increase in the positive electrode efficiency could be achieved by reducing the thickness of the usual 4BS cured industrial samples from 10–15 to 3–4 μm.

Structural memory effect in liquid crystal phases stabilised by silica particle aggregates

A SANS study revealed the orientational stabilisation of the smectic structure by non-mesogenic polymer networks dispersed in a liquid crystal matrix. In the present experiment, hydrophobic silica particles were dispersed in liquid crystal 8CB. The Bragg reflections from smectic layers show that the alignment of the layers is perfect if the system is cooled down in a magnetic field. After annealing without magnetic field and cooling down to smectic A phase, the previous alignment of the liquid crystal is recovered. Temperature and concentration dependence of the effect has been analysed by recording the diffraction pattern from smectic layers.

96/04270 Minimising corrosion of copper tubing used in refrigeratiion systems

Layered double hydroxide (LDH) has been widely developed in the field of corrosion and protection in recent years based on its unique characteristics including anion capacity, anion exchange ability, structure memory effect, and barrier resistance. This paper comprehensively reviews recent work on the preparations, properties of LDH in the forms of powder and film and their applications in different environments in corrosion and protection. Some novel perspectives are also proposed at the end of the review for future research in corrosion and protection field.

The Martensitic Structure and Shape Memory Effect in NiMn Alloyed by Ti and Al

Structure and mechanical properties of the intermetallic compound NiMn alloyed by Ti and Al have been studied using optical and transmission electron microscopy, X-ray diffraction and dilatometry. Alloying has been found to reduce the temperature of β ↔ θ martensitic transformation, the martensite tetragonality and the transformation volume effect. Ti/Al alloying improves ductility of NiMn due to a high density of mobile stacking faults and heterophase microstructure. The partial shape memory effect has been observed by bending NiMn-Ti/Al strips.

Reversible amorphization and structural memory effect in clathrasil dodecasil-3c

Abstract The mechanism for the novel structural memory effect, where a crystalline solid compressed to an disordered phase is able to revert back to the original crystal structure upon the release of the pressure, is investigated using clathrasil dodecasil as a model system. It was found, through experiments and theoretical molecular dynamics calculations, that the presence of undeformable units, such as the guests, are essential for the reversible process. The transformation of the clathrasil to a high density disordered structure at high pressure is due to a mechanical instability. In the absence of atomic diffusive motions, when the pressure is relieved the encaged guests act as templates and redirect the atoms collapsed around them back into the original structure.

Theoretical studies of structural stability at high pressure

Theoretical methods are indispensible for the study of matter at high pressure. In the last decade the development of accurate intermolecular potentials and the methodologies in classical molecular dynamics (MD) simulations have greatly facililated the applications of these methods to the study of structural phase transformamtions of solids at high pressures. More recently, it has been possible to incorporate quantum mechanical effects into MD calculations. This method eliminates a great deal of empiricism. These first principles calculations have not only reproduced the experimental results for phase transformations but also provided detailed mechanisms and in some cases predicted new structures that may be found at high pressures. The success of MD calculations is illustrated through a review of our studies of pressure-induced amorphization and phase transitions in SiO2 and TiO2, and the structural memory effect in several materials. Current applications using quantum molecular dynamics on ice are discussed.

Structural phase transformation and shape memory effect in ZrRh and ZrIr

Crystal structure investigations of the ZrRh and ZrIr compounds have shown the occurrence of a B19'-type phase at room temperatures, a B2-type phase at 670 and 1050 °C respectively and a b.c.c. phase for ZrRh in the temperature interval from 1455 °C to the melting point. The shape memory effect was observed for ZrRh and can be expected too for ZrIr in view of the very similar transformation characteristics of ZrRh and ZrIr.

Structural Memory Effects in Rapidly Quenched Iron-Boron-Based Glassy Alloys

Structural Memory Effects in Rapidly Quenched Iron-Boron-Based Glassy Alloys

Infrared spectrometric study of poly(vinylidene fluoride) films in cyclic electric fields

Infrared spectra of uniaxially drawn β-poly(vinylidene fluoride) films were recorded under the influence of an electric field. The direction and strength of the applied field were changed in up to thirteen cycles with a maximum field strength of 240 MV m −1. The field-induced changes of the absorbances of the bands at 445 cm −1 (CF 2 rocking) and at 510 cm −1 (CF 2 bending) were evaluated. Certain amounts of 180° switching and a structure memory effect are discussed to explain the experimental results obtained for repeated repoling processes.