The formation of ordered phases of acid-hydrolyzed cellulose suspensions was studied as a function of cellulose crystallite concentration and added electrolyte (HCl, NaCl, and KCl) concentrations. A chiral nematic phase formed when the suspension concentration was higher than 5.14 × 10-6 nm-3 in water. For biphasic samples, the cellulose concentrations in both isotropic and anisotropic phases increase with the total suspension concentration and with added electrolyte. The experimental results were compared with the predictions of the theory of Stroobants, Lekkerkerker, and Odijk for the phase separation of charged rods. The suspensions were not stable at electrolyte concentrations sufficiently high to allow complete evaluation of the electrostatic contribution to the interparticle interactions, but the general behavior was in line with theoretical predictions. The chiral nematic pitch of the anisotropic phase decreased with increasing crystallite concentration and with added electrolyte concentration. Apparently, a decrease in double layer thickness increases the chiral interactions between the crystallites.

ABSTRACT:This paper reviews our recent work on the use of magnetic fields to the polymer processing. Polymers considered in this paper are not peculiar ones synthesized specially for the purpose of magnetic processing, but they are very usual ones including poly(ethylene terephthalate), polypropylene, etc. In this paper, two main magnetic effects on polymers are considered, i.e., alignment and levitation. In the first part, the magnetic torque causing the alignment is described. Then, examples of alignment in polymeric systems are presented, starting from simple cases such as magnetic alignment of fibers in a suspension to more complicated cases such as magnetic alignment of crystalline polymers in which mesophase formations and memory effects are involved. In the second part, the magnetic force acting on diamagnetic materials and its application to separation and processing of polymeric materials is described.KEY WORDS Diamagnetism / Magnetic Alignment / Magnetic Levitation / Phase Transition / Crystalline Polymers / Polymer Processing / Fiber / Magnetic effects on diamagnetic materials have been known since the age of Faraday, but it is very recent that the attention has been paid to the use of these effects to the processing of diamagnetic materials including inorganic, organic, and polymeric materials. This trend is partially due to the development of superconducting technology 1 that enables us to use high magnetic fields (10 T or more) in the study of materials science at individual laboratory level. Cryogen free (liquid-helium free) superconducting magnets, mostly manufactured by Japanese companies, are now on the market, with various types including a large bore type (45 cm at 3.5 T), a rotate bore type, a split type, a low fringe field type, a high field type (15 T, 52 mm in diameter), etc. These magnets are used in academia as well as industries for the processing purposes.High magnetic fields provided by these superconducting magnets have made it possible to visualize the magnetic effects on "non-magnetic" materials such as diamagnetic materials. Because the diamagnetism is very small compared to the ferromagnetism, we hardly experience in daily life the effects of magnetic field on plastics, water, and living bodies, etc. Some means must be devised to visualize these effects. A straightforward way is to use high magnetic fields. If we use a superconducting magnet of 10 T instead of an electromagnet generating 1 T, a small change of 1 mm is magnified to 10 cm and a phenomenon that takes a day to occur is completed in 15 min, because the magnetic effect is proportional to the square of the magnetic flux density. Diamagnetic levitation 2-4 and Moses effect 5 (water surface splits in a high magnetic field) are good examples among many others. [6][7][8][9] The magnetic effect on chemical reactions 10-12 is one of the major fields in magnetic researches, but in this paper we are concerned with the magnetic force and the magnetic torque acting on diamagnetic materials. The origin of the diamagnetism is the ...

Stable suspensions of tunicate cellulose microfibrils were prepared by acid hydrolysis of the cellulosic mantles of tunicin. They formed a chiral nematic phase above a critical concentration. External magnetic fields were applied to the chiral nematic phase in two different manners to control its phase structure. (i) Static magnetic fields ranging 1-28 T were used to align the chiral nematic axis (helical axis) in the field direction. (ii) A rotating magnetic field (5 T, 10 rpm) was applied to unwind the helices and to form a nematic phase. These phenomena were interpreted in terms of the anisotropic diamagnetic susceptibility of the cellulose microfibril. The diamagnetic susceptibility of the microfibril is smaller in the direction parallel (chi( parallel)) to the fiber axis than in the direction perpendicular (chi( perpendicular)) to the fiber axis, that is, chi( parallel) < chi( perpendicular) < 0. Because the helical axis coincides with the direction normal ( perpendicular) to the fiber axis, the helical axis aligned parallel to the applied field. On the other hand, the rotating magnetic field induced the uniaxial alignment of the smallest susceptibility axis, that is, chi( parallel) in the present case, and brought about unwinding of the helices.

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A theoretical study has been presented to show that it is possible to align three different diamagnetic susceptibility axes (chi(3) < chi(2) < chi(1) < 0) of a crystallite with respect to the laboratory coordinate system (x, y, z). The time-dependent magnetic field that periodically changes in direction and intensity on the xy plane in an elliptic manner (the intensity stronger in the x direction) at a rate quicker than the intrinsic rate of magnetic response causes the three-dimensional alignment, that is, chi(1) parallel x, chi(2) parallel y, and chi(3) parallel z. The fluctuation of the three susceptibility axes around the corresponding laboratory coordinates is estimated in terms of the fluctuation around the minimum of the time-averaged magnetic potential. This technique enables the three-dimensional alignment of the crystallographic axes.

The powder crystallites of L-alanine, selected for demonstration purposes, suspended in a photocurable resin were subjected to a frequency-modulated rotating magnetic field, and the achieved three-dimensional alignment was fixed by photopolymerization of the resin. The obtained sample exhibited the X-ray diffraction pattern that was comparable to the pattern of an equivalent actual original single crystal. This was achieved for the first time by the simultaneous alignment of the two magnetic axes, i.e., the easy and hard magnetization axes with respect to the space coordinates. A theoretical estimation indicates that a better alignment of the sample can be obtained if the sample preparation conditions are improved.

A diamagnetic particle with magnetic susceptibilities χ3 < χ2 = χ1 < 0 was subjected to a rotating magnetic field to obtain an alignment of the χ3 axis (the smallest susceptibility axis) in the direction perpendicular to the plane of the rotating magnetic field. A polymer short fiber, whose fiber axis coincides with the χ3 axis, was suspended in a fluid with the same density, and then a rotating magnetic field generated by a rotation of a pair of permanent magnets was applied. The fiber axis, rotating following the applied field, finally ended up with an alignment perpendicular to the plane of the rotating magnetic field. The experimental data on the time course of the alignment was in good agreement with the numerical calculation based on the equation of rotation.

Nanorods of La@C82(Ad) (Ad = adamantylidene) were prepared via the liquid−liquid interfacial precipitation method. From the SEM, HRTEM, EELS, and SADEP analyses, it was revealed that the nanorods consist of a single crystal of La@C82(Ad). The field-effect transistor (FET) measurement of the La@C82(Ad) nanorods shows a p-type action. The magnetic orientation of the nanorods was observed; that is, the nanorods of La@C82(Ad) oriented with the nanorod axis perpendicular to the magnetic field.