## 1 Introduction  
The orientation of liquid crystals (LCs) is highly sensitive to the nature of the substrate surface. This property is particularly significant for the fabrication of LC display panels and other optical devices. Recently, photoalignment technology has become important as an alternative to the rubbing process in LC display panel production. Photoreactive polymer layers that respond to linear polarized light or diagonal irradiation light are usually used in these processes [1, 2, 3, 4, 5, 6, 7, 8, 9]. As related systems, photoalignable side chain liquid crystal polymers (SCLCPs) have been widely studied in the fabrication of optically functional devices [10, 11, 12, 13] and light-driven mechanical elastomer films [14, 15, 16, 17, 18]. SCLCP films are mostly prepared by the spin-coating procedure. In spin-coated films, one side of the film is supported by the solid substrate surface, and the other side contacts the air (free surface). It has recently become evident that the free surface plays an essential role in the mesogen orientation on SCLCP films [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27]. The existence of a top layer on SCLCP films strongly influences the mesogen orientation. Such an effect has occasionally been discussed in block copolymers possessing an SCLCP block to control the orientation of the microphase separation (MPS) structure [19, 20, 21]. [PERSON] et al. [19] showed that a vertically aligned MPS structure turns into a planar one when a surface segregated layer exists on the top surface. [PERSON] et al. [20] showed that a homeotropic LC and cylindrical MPS structure is changed to a planar one when the film is covered with silicone oil. [PERSON] et al. [21] indicated the orientation control of a cylindrical MPS structure by converging the top surface with a water-soluble polymer. Other than SCLCPs, coverage of the free surface of amorphous block copolymers such as poly(styrene-_block_-trimethylsilylstyrene-_block_-styrene) was conducted by [PERSON] et al. [28]. They adopted a polarity-transformable topcoat to attain the vertical orientation of the MPS, which is essential in the block copolymer lithography. For simple SCLCP systems without an MPS structure, [PERSON] et al. [23] demonstrated that the homeotropic orientation of a light-passive SCLCP film is altered to a planar one when the top surface is covered with an azobenzene (Az)-containing polymer via annealing-assisted surface segregation or inkjet printing. This system provides a photopatterning of the birefringent character of the whole film, indicating that the top photo-toalignable layer can command the whole light-passive SCLCP film existing underneath. Shortly after this approach, [PERSON] et al. [24] demonstrated that the mesogen orientation of a light-passive SCLCP film can be switched repeatedly by alternative light irradiation to a surface-segregated Az SCLCP existing on the surface. This system can be compared with the original photo-switchable alignment system achieved by an azobenzene monolayer on a solid substrate called the \"command surface\" [1,29,30]. [PERSON] et al. [25, 26, 27] proposed a smart strategy to use low molecular mass molecules to modify the top surface. By deposition of an aromatic amine onto a benzaldehyde-containing side chain polymer film, the side chain reacts with the aromatic amine to form photoaliignable \(N\)-benzylideneaniline. After photoalignment is attained, the top layer can be removed by heat-assisted sublimation. Therefore, the photoalignment ability can be switched or fixed on demand. Rod-like mesogens tend to be anchored to the solid surface and free surface horizontally (planarly) [31, 32, 33] and vertically (homeotropically) [34, 35, 36, 37, 38] in relation to the interface plane, respectively, due to the excluded volume effect. The orientation alternations for SCLCPs, as mentioned above, can be understood in line with these theoretical and experimental facts.