Polarization and pitch dependence of cholesteric blue-phase structures

On the effect of alignment layers on blue phase liquid crystals

“…10,11 Such a graph is shown in Figure 4 discontinuity of $65 nm in k 0 is consistent with previously reported values involving phase transition from BPII to BPI. 6,12 Smaller peaks around 440 nm below 42.7 C correspond to a N* phase.…”

The liquid-crystalline blue phases

“…The variation of the dominance of the two phases with chirality is similar to the behaviour found by Marcus and Goodby (1982) (figure 19(b)); the polarised light results of Flack and Crooker (1981) and Flack et a1 (1982) are accounted for, as well as some of the morphological features found by Onusseit and Stegemeyer (1981).…”

“…Nevertheless, the high-chirality (single spatial frequency) limit, which was initially treated exclusively Shtrikman 1979, 1980a, b), is evidently inconsistent with a large number of the early experimental findings detailed in section 3: in particular, the appearance of more than one cubic structure (Bergmann and Stegemeyer 1979a); the red shift of the primary reflection (Bergmann et al 1979); the observation of a second strong Bragg reflection for both BPI and BPII (Goldberg and Schnur 1970, Meiboom and Sammon 1980, Johnson et al 1980, indicating as shown below that neither has an O5 structure; and even more definitely the polarised light studies (Flack and Crooker 1981), which found the second Bragg line strongly sensitive to the sense of input light. The last result seems to rule out the O5 symmetry for which the c = 2 reflection is polarisationindependent in the back direction (see below).…”

“…Many qualitative features of the BPS are well accounted for by the asymptotic model described in the previous section: the relative narrowness of the BP region (1-2 K), the narrowing with increasing pitch (decreasing K ) , and optical properties such as the absence of birefringence (Pelzl and Sackmann 1973, Demus et a1 1978), the optical activity Sammon 1980, 1981) and gross features of the Bragg spectra , Goldberg and Schnur 1970, Meiboom and Sammon 1980, Johnson er a1 1980, Flack and Crooker 1981, Marcus and Goodby 1982, Marcus 1982a and N M R spectra (Samulski andLuz 1980, Yaniv et a1 1983), which are common to all cubic phases. Nevertheless, the high-chirality (single spatial frequency) limit, which was initially treated exclusively Shtrikman 1979, 1980a, b), is evidently inconsistent with a large number of the early experimental findings detailed in section 3: in particular, the appearance of more than one cubic structure (Bergmann and Stegemeyer 1979a); the red shift of the primary reflection (Bergmann et al 1979); the observation of a second strong Bragg reflection for both BPI and BPII (Goldberg and Schnur 1970, Meiboom and Sammon 1980, Johnson et al 1980, indicating as shown below that neither has an O5 structure; and even more definitely the polarised light studies (Flack and Crooker 1981), which found the second Bragg line strongly sensitive to the sense of input light.…”

‘Blue phases’ of highly chiral thermotropic liquid crystals with a wide range of near-room temperature

“…It is known that for certain chiral liquid crystals (CLCs) and their mixtures the transition between the regular (helical) cholesteric phase (Ch) and the isotropic phase (Iso) occurs through a series of additional transitions well known as 'blue' phases (BPs), [1][2][3][4][5][6][7][8][9] which in most cases can exist only for cholesterics with pitch P < 5000 Å. [5,10] Within a narrow temperature range three thermodynamically stable blue phases (BP-III, BP-II and BP-I) exist, which can be usually observed on cooling from Iso to Ch, but sometimes on heating from Ch to Iso [3,9,11] and vice versa with thermal hysteresis.…”