Перевод строки в посимвольный массив с поддержкой UTF-8

string_split_unicode.php

$string = "ЧелоБрейк";
function string_split_unicode($string, $length = 1) {
    $tmp = preg_split('~~u', $string, -1, PREG_SPLIT_NO_EMPTY);
    if ($length > 1) {
        $chunks = array_chunk($tmp, $length);
        foreach ($chunks as $i => $chunk) {
            $chunks[$i] = join('', (array) $chunk);
        }
        $tmp = $chunks;
    }
    return $tmp;
}
print_r(string_split_unicode($string, 1));